Tips to Use Dazzle (Dota2)

• Don't forget that Shadow Wave deals damage around your healed allies as well, roughly a Melee hero swing and a tiny bit more; a bit similar to Omniknight's Purification but with considerably less raw healing.

• Each level of upgrade for Shallow Grave makes it cost less mana; if you're having mana problems (and you likely will), consider upgrading it sooner rather than later.

• Your first skill can be any of the three depending on the situation; Poison Touch if you're hunting for first blood (with teammates, by yourself or with a single lane partner is probably not enough and can be risky in the event of a reversal), Shallow Grave if the enemy has not been spotted in their lanes and you suspect a possible gank incoming, and Shadow Wave if you're fighting an aggressive melee gank with an ally.

• Don't forget that the range of Shallow Grave increases with each level; it starts out less than your normal attack, but at level 4 goes to twice that length. You don't want to have an ally die just because you had to run in closer.

• Using Shallow Grave is the most important role Dazzle has, and one of the chief reasons why Dazzle is complicated; in using it you grant an ally or yourself five seconds where they cannot die. For newer players, it is often better to use it earlier than never; 2 seconds of life for an ally is better than none. More experienced players can gauge the situation of battles better, and can determine if burst damage has already been applied, amount and length of incoming stuns, and at whom they're directed, et cetera. In the early game laning phase, you can aggressively attempt a kill and then use Grave on yourself once you're near death; however, this can easily backfire due to burst damage and stun, preventing you from using the spell. In the mid game, your priority to grave are heroes with powerful abilities that haven't been used yet in an encounter, such as a Sand King Epicenter, a Tidehunter's Ravage, or an Enigma's Black Hole. Typically, the use of such ultimates would change the tide of battle in your favour, although this would only apply if those types of heroes are caught out of position, or are about to die before they can use it. Preventing a hard carry from dying and losing their gold is also important, but not if it means losing the teamfight and being able to push. In late game, keeping your hard carry alive becomes your top priority. There may be instances wherein you must choose between the life and death of allies, and it is very important to know who to prioritise (knowledge of priority will become second-nature with experience). For example, choosing between keeping Tidehunter alive after his Ravage has been used is a poor decision versus keeping your team's Lycan from dying, but if Tidehunter's death seems to be sure and Lycan's does not, you must make a decision very quickly. This is the difficulty of Dazzle.

• While Weave is a spell with a fairly simple effect it can massively increase both the deadliness and the durability of your team, especially if it is heavy in physical damage dealers who need to close with the enemy like Ursa and Sven.

• Learn to use Weave pre-emptively to maximise the armor buff/debuff for the team fight. In addition, it can be used to discourage your enemies from sieging a tower or attempting Roshan: as their armor deteriorates while they make an attempt, their chances of following up with a team fight in their favour becomes much lower. 

source: http://dota2.gamepedia.com/Dazzle

Tips to Use Sven (Dota2)

• Early on Sven has very low mana, so building mana boosting items may be a good idea.

• Drum of Endurance is a great item as it meshes well with Sven's role and play style.

• Take Stats over the two other skills instead if you want more Mana, Attack Speed and Strength to increase the bonus of God's Strength early on and to help sustain your mana for using skills. However, this is only useful very early on, as Warcry is amazing for teamfights and Great Cleave helps Sven's farming speed.

• If you prefer to initiate, get a Blink Dagger. Blink to your target and stun them with your Storm Hammer, make sure you activate God's Strength immediately or beforehand, which is more preferable as you can save more time on the casting animation and transformation time.

• Avoid leveling Great Cleave early on, as it will greatly push the lane towards the enemy tower making farming more difficult.

• As a melee carry without a blink, Sven is especially susceptible to being kited and having crowd control effects placed on him, negating his damage output. Don't skip Black King Bar to buy more damaging items, as it may result in doing no damage at all.

• Sven's unique position of being a Support and Carry at the same time, can make him a decent babysitter for a ranged carry like Weaver, Luna, or Sniper. Build arcane boots to give you and your lane partner more mana, so you can pop your Storm Hammer and Warcry more often, and focus on massing gold once your carry has had his fill, this can put you in a situation of having 4 fed carries on your team, giving your team a bigger edge on long extended games, altough it can be difficult to pull off, so use this tactic carefully. 

source: http://dota2.gamepedia.com/Sven

Tips to Use Warlock (Dota2)

• Consider going solo lane if your team wants to try an early push strategy. Warlock's attack range, projectile speed, and damage allows him to farm nicely against other solo heroes.

• Shadow Word can also be used as a harassing tool. Cast it on your opponent and keep hitting him whenever it's possible. Make sure you don't get hit by creeps too much while doing so.

• Fatal Bonds is an immensely useful spell which amplifies your team's damage output. Bond 5 enemies together, and if they are all hit by a single area of effect spell or attack, the total damage will be almost doubled, since everyone of them will suffer 4x20% extra damage echoed from others.

• You can use Upheaval to prevent wounded enemies from escaping. This is especially useful if used right after an area-of-effect spell, such as your Chaotic Offering. Let your golem or your teammates finish the job.

• During teamfights later in the game channeling Upheaval aids your team more than attacking; after casting Fatal Bonds and Chaotic Offering begin channeling Upheaval immediately to maximize its slowing effect and the amount of damage done by your team and golems.

• If an ally is being chased, use your Upheaval to slow his chasers. Since the slow will last for some seconds after you stop channeling, you will also have time to fall back.

• When initiating, make sure to cast Fatal Bonds first, then Chaotic Offering; this way, you can output more damage against all your targets.

• Your golem is tanky; when possible, use it to tank creeps or towers, so that you can dispose of them sooner.

• You can heal the golem with your Shadow Word to increase its tankiness.

• When chasing fleeing heroes with your golem, don't stop to auto-attack them, since it will slow the golem down. Instead, keep it moving with the heroes, so that the Permanent Immolation can do its damage.

• Although both Refresher Orb and Aghanim's Scepter allow you to summon two golems, Refresher Orb allows you to summon two full strength golems and utilize two seconds of AoE stun, but will cost a lot of mana to pull off, while Aghanim's Scepter is easier and cheaper to build and gives nice stats. having both items will let you summon 4 golems at the same time.

• Do not let the golem die needlessly to your enemy heroes, since its gold bounty is quite high. If it's the last remaining unit for your team in a fight, have it flee unless you can ensure a kill. Having it die against creeps or towers is better than allowing an enemy hero to claim the gold bounty of your golem. Having two golems from Aghanim's Scepter will cut the bounty of each golem in half.

• Fatal Bonds and Venomancer's Poison Nova make for a deadly combination, as although Poison Nova cannot kill on its own, Fatal Bonds will cause anyone bound and affected by the poison to die from the damage ticking off.

• Remember your role: as a support Hero, you should be leaving as much experience and gold as possible to the carry. While items like Aghanim's Scepter and Refresher Orb may seem so powerful, it's advised not to buy them too early, or not to buy them at all: concentrate on buying Wards, Dust and utility items like Mekansm, Force Staff, Necronomicon, Drum of Endurance or Eul's Scepter of Divinity first. Even Wards and Mekansm alone will certainly be more useful than a Warlock who stole kills from the carry, leaving him underfarmed and underleveled. Only acquire kills if the carry is unable to do so. 

source: http://dota2.gamepedia.com/Warlock

Tips to Use Gyrocopter (Dota2)

• Rocket Barrage is incredibly powerful against a single enemy, but its damage falls off dramatically if there are multiple targets. Position yourself to make the best use of it.

• Homing Missile is a great harassment tool. Place it behind your allies to prevent the enemy from destroying it before it starts moving.

• Flak Cannon allows you to harass enemy heroes from a great distance, or force them away from the creeps. An early point should be considered if you are taking the solo mid-lane. However, it does push the lane and may open yourself to ganks.

• Using Flak Cannon early (before you use the attacks) will lessen the cooldown on your next cast.

• For maximum effect, cast Call Down in conjunction with your Homing Missile's impact or an allied disable.

• Aghanim's Scepter will allow you to snipe fleeing enemy heroes with Call Down. It can also be used to assist or deter pushing. 

source: http://dota2.gamepedia.com/Gyrocopter

Tips to Use Tusk (Dota2)

• When being pursued by numerous heroes, you can cast Ice Shards toward them to hinder their movement, as the barrier forces them to break up and even come to a slight halt. It is ideal to cast Ice Shards when your pursuers are in a small choke-point, as the barrier will most likely block their way, or at least make it even more difficult for them to move forward.

• Ice Shards' missile cast is delayed; keep this in mind when you are targeting distant, fleeing heroes.

• When pushing, defending, or farming, Ice Shards is an effective area-of-effect skill you can use to damage multiple creeps in a straight path; unlike target heroes, Ice Shards doesn't create a barrier when it contacts creeps.

• Aid your team's initiator by pairing up with him/her and casting Snowball on the group of enemies; the movement makes both Tusk and his teammate invulnerable, and any target that is hit by it gets stunned for a brief second, giving the initiator some time to act.

• Be careful when using Frozen Sigil, as it gives a large bounty when destroyed. Only direct it toward enemy heroes when they are too busy to pay attention to it (i.e. when being pursued by your allies). It has a relatively fast speed and can catch up to most enemies.

• Purchase mana boosting items to supplement all of your four active spells, since Tusk is incredibly skill-dependent.

• Walrus Punch deals 4x critical damage when enemies are 50% below their maximum health. Similar to Bounty Hunter's Jinada, it also maims the target to a crawl, so use this to knock out an enemy before they can retaliate. However, this move can accidentally steal the kill due to its potential critical damage, but nevertheless it is acceptable, since Tusk benefits from additional items.

• If you managed to get quite some gold from ganks early on, you could consider going for armor-reducing items like Medallion of Courage or Desolator: they give amplified damage for a reasonable price. Just be sure to use your Medallion on the enemy before utilizing your ultimate on him.

• If you find yourself without mana too often, you could consider going for Arcane Boots or Intelligence-boosting items like Drum of Endurance or Force Staff, which also come with nice abilities. Alternatively, you could buy items that increase your mana regeneration such as Medallion of Courage and Perseverance (which can also be turned into a Battle Fury, should you get other damage-increasing items before finishing the whole item). 

source: http://dota2.gamepedia.com/Tusk

Tips to Use Crystal Maiden (Dota2)

• Crystal Nova is a large area of effect nuke that also slows your enemies. You can hit enemies from 1100 units away with it (700 casting range + 400 radius).

• Frostbite is a great disable which prevents the target from moving or attacking. It also interrupts channelling spells and teleports. Unfortunately, it does not prevent enemy heroes from casting spells.

• Arcane Aura used to be prioritized as it benefits the whole team greatly, especially one with a strong caster/ganker line-up. But the introduction of Arcane Boots has made this skill somewhat less useful.
  • Since 6.76 this bonus is doubled on Rylai herself, granting a whopping +5 bonus mana/s.

• Freezing Field is an incredibly strong spell. However, it can be unpredictable and usually gets interrupted by your enemies very quickly. Freezing Field consumes a lot of mana, so use it sparingly.
  • Many players choose not to skill Freezing Field until quite late in the game, as it is a situational spell that is most effective in large clashes; and its use consumes a huge amount of mana. However, its slow and gigantic (if unpredictable) damage can be very useful in early game, especially against enemies that lack the means to interrupt it. Let your decision be informed by enemy lineup as well as laning composition.

• Items like Black King Bar and Shadow Blade are viable options to prevent your opponents from cancelling your ultimate, but Crystal Maiden usually won't have that much gold to spend.

• Crystal Maiden can either babysit her team's carry on dual/triple lanes, or roam between the lanes to gank enemies.

• Always ward the woods. Wards should be bought over and over again to provide map control through the whole game.

• There is a temptation to use Crystal Nova to push lanes, but owing to its mana cost and long cooldown this isn't a good idea.

• If you have a few coins to spare - always buy items that boost your survivability, or get yourself an escape/positioning mechanism like Blink Dagger or Force Staff.

• Freezing Field must be used at the right time to avoid interruption and being focused. Generally speaking, in an encounter it is best used after the initial nuking phase; when the enemy's stuns are on cooldown (building a Black King Bar will provide immunity to stuns; but Crystal Maiden does not typically get much gold and this can be very difficult to build in a game where your team is not getting a lot of kills). If your team has an initiator with the capability to disable a group of enemies, such as Tidehunter or Enigma, Freezing Field should be used in synchronisation with their mass disable. Using Freezing Field very often results in Rylai's death, and she rarely is able to channel it for its full duration, but if she can maintain it even for a few seconds it will be useful for her team.
  • Although Freezing Field's damage can be upgraded with Aghanim's Scepter, its primary use is its slow rather than its damage and considering Rylai's low gold income, building Scepter is typically not a good idea; her ult would be more useful if instead she built Black King Bar and/or Blink Dagger and typically of a support hero she normally must choose only a couple of luxury items. 
   

source: http://dota2.gamepedia.com/Crystal_Maiden

Tips to Use Luna (Dota2)

• Luna and Night Stalker complement each other well; as Eclipse causes day to become night and Darkness gives both of them a very long vision range.

• Early points in Lunar Blessing will make last-hitting creeps easier. At any rate, make sure you have a single point in it before the first night as only one point is needed for the full amount of vision it bestows.

• Early points in Moon Glaives will push the lane. Moon Glaives is commonly not skilled at all until the laning phase has concluded.

• Extremely unusually for a hard carry, Luna gains significant killing power with a level advantage, owing to Lucent Beam and by extension Eclipse.

• Lucent Beam's cast range is gigantic. Use it to pick off fleeing heroes.
  • Bear in mind Eclipse's range is much smaller than Lucent Beam's.

• Under almost all circumstances Luna should be paired with a disabler for her laning phase; as aside from her high movement speed she has absolutely nothing to help her avoid ganks or kill attempts.
  • It takes significant skill and knowledge of the game to solo a lane with Luna. Her very small attack range and purely damage-oriented skillset mean she is extremely easy to kill. Even then, it is recommended to have ward vision and easy access to team backup for her to be successful in a solo lane. The advantage of running a solo Luna is that it is essentially high-risk high-reward. A Luna with level advantage doing well can easily set the momentum of the game in her team's favor. 
   

source: http://dota2.gamepedia.com/Luna