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