Tips to Use Skywrath Mage (Dota2)

• Skywrath Mage needs to control the spacing between him and his opponents carefully. Skirt the outside of the fight and slow and silence enemies that attempt to shut you down, everything you can do has very long range and your turnspeed is very fast.

• The amplification of magic damage couples nicely with arcane bolt's bonus intelligence damage. Ancient Seal also silences your target, so use this to net kills early game.

• Arcane Bolt deals a lot of damage at level 1 to level 1 heroes. When coupled with Intelligence bonus items like Mantle of Intelligence, even more damage is dealt. The mana cost is also very low, so it's a wonderful harrassment tool. It will also make last-hitting an easy task when you have some good mana regen going.

• Skywrath Mage is a very squishy hero, so HP items are commonly built. When laning or in a teamfight, try to stay out of range of enemy auto-attacks, and use your skills from a distance, only jumping in when necessary. Force Staff solves this problem easily, allowing a quick escape if danger arises.

• Mystic Flare is much more efficient on single heroes during ganks, since they receive the full, undistributed damage amount. Try to use this with an ally's stun, however, as the AoE is very small, and very easy to escape out of when not disabled. Using Mystic Flare during a teamfight isn't a bad idea, but it only really works if all the enemies are stunned by a large AoE teamfight Ultimate, such as Magnus's Reverse Polarity. Mystic Flare can be used to kill off the remaining heroes after the stun has been successful.

• Rod of Atos can be a good early-mid game item, as it gives health and Intelligence: you will be more difficult to kill, and your Arcane Bolt will deal even more damage. Furthermore, the slow can be used to set up a perfect Mystic Flare.

• You will need to be extremely careful when facing heroes that can deal damage based on your mana pool or intelligence. Examples of this include Pugna's Nether Ward, Anti-Mage's Mana Void and Nyx's Mana Burn. If these heroes are giving you trouble, you may even wish to consider a Black King Bar of your own later in the game to keep you protected from these powerful counters during teamfights.

• It is common to begin ganking at level 6. Skywrath Mage needs all the farm he can get for his core items and all the experience for more levels, which equal more intelligence.

• Skywrath Mage's killing combo is to initate Ancient Seal, then attack with Concussive shot. Follow up with Mystic Flare and some Arcane Bolt's to finish them off. Most supports and squishy heroes like Sniper will drop right after Mystic Flare and one or two Arcane Bolts.

• It is best to lane with heroes with stuns like Vengeful Spirit, Lion or even Alchemist. Stuns guarantee that Skywrath Mage will be able to land his Mystic Flare. Similarily, Heroes with long lasting disables like Shadow Shaman can hold them in place long enough for Skywrath to hit them with some Arcane Bolt's and Mystic Flare. 

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