Tips to Use WIndranger (Dota2)

• If you must solo a lane, take Windrun first. This will give you a reliable escape if you are being ganked early.

• Power Shot should always be maxed first, as it is a very powerful nuke early. One point in both Shackle Shot and Windrun is usually sufficient. Remember that Power Shot damages invisible heroes, so if you know where they are do not hesitate to use it. Late-game, Power Shot can be used as an exploratory long-range spell.
  • Power Shot claims to do reduced damage if released early, but releasing it at 60% or more inflicts full damage.

• Despite it being unlisted in her recommended items, Mekansm is very strong on Windranger. Consider getting it on her after your upgraded boots, provided no one else can get it at a similar time. Remember, Mekansm is better the earlier it's gotten.

• Shackle Shot's ministun is extremely useful for interrupting channeled spells, such as Bane's and Pudge's ultimates.

• Early-game, unless circumstances are unusual, always save enough mana to Windrun when you are in dangerous territory.

• Due to the rework of Focus Fire, it might be useful to level it early, as it is now more useful in teamfights, allowing you to focus down the enemy carry, be wary of the mana cost though, as using it might leave your mana too low to cast your other spells, which are more useful in most cases.
• Despite being an escape mechanism, Windrun is potentially a very powerful defensive spell, as it allows complete immunity against damage from physical attacks.

• Building an Aghanim's Scepter with a powerful attack modifier can shift Windranger's role from supportive chaser/nuker to that of a semi-carry, as it will allow her to scale. However, building a scepter without an attack modifier is not very useful, and Windranger can function very well with attack modifiers even without building a scepter. Build an attack modifier first, then choose whether or not to build scepter. 

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