Level 1 you will take the talent Corruption for knocking out ammo charges on towers and forts. This both helps your minions push faster, but most importantly it will help your team and even mercenaries push faster by not taking hits from them. When you drain one target of ammo switch to the next, then the next. If it is a tower set with a gate then drain the towers and kill the gate after that. Why? because assuming no one stops you (usually they do) you can easily push into the fort and start draining it too. The point here is to keep depleting and keep making yourself a pain in the *** for the enemy so they either have to allocate team members to stop you weakening their offense or leaving you alone to totally wreck them.

At Level 4 you will take Ranger's Ambush to recharge your Withering Fire stacks. This may take getting use to. However, the general idea is like this. You use Haunting Wave to teleport normally as an escape. This talent changes that to a chase or sort of side-step skill to refill you charges and keep firing.

Level 7 is Unstable Poison. This talent will help you a lot in minion clearing since anything affected by your black arrows (basically all your attacks) explodes on death.

On Level 13 you will want to pick up Splinter Shot so that your Withering Fire will fire at two targets.

For Level 16 I would say that Cold Embrace is probably mandatory for a lot of builds. Maybe I am wrong though. The mass vulnerability is just too good to pass up though even at the reduction of range.

Your Ult and upgrade for 10 & 20 are going to be Possession and Dark Lady's Call. The Level 10 will allow you to start turning their own minions against them. What this does is basically push their lanes by doubling your minion wave. At 20 you can even take control of up to 2 mercenaries. Typically you would use this on giants but it can be used on anything. For example a knight pack is 4 mercs. You would take control of 2 and kill the rest.

Level 1 you will take the talent Corruption for knocking out ammo charges on towers and forts. This both helps your minions push faster, but most importantly it will help your team and even mercenaries push faster by not taking hits from them. When you drain one target of ammo switch to the next. Unlike the "Lane Push" build which can build up to really pushing things with Corruption later this build won't. So you won't want to focus a lot on it. You will want to do the same thing though to help your team and minions push, but its not going to be a primary goal, mostly a secondary one when you are between phases and can hit them.

For Level 4 you want to grab Paralysis to make your Black Arrows last longer. This wont help you immediately but later it will.

At Level 7 you will pick up Remorseless which will give you basic attack damage. This is a key part of your damage in "team fights" and will take a LOT of getting use to. As you will notice it says "after using an ability". The key thing here to remember is ability management. You have your Haunt, Dagger, and Withering abilities. Withering Fire is the key here because it has 5 charges. The hypothetical ideal rotation would be.. Ability > Basic > Ability > Basic > Ability > Basic... and so on. Things dont always work out in real fights and you do what you can. Just remember each charge is an "ability" cast.

Level 13 you will want Overwhelming Affliction. This is where the previous talent into Paralysis starts helping you.

At Level 16 you pick the required Cold Embrace to cast mass vulnerability making the enemy take more damage.

For your Level 10 and 20 you will take Wailing Arrow and Deafening-Blast. This gives you a silence which is useful in interrupting most enemy casts and in team fights it can help a coordinated group quickly turn the fight around. Note though, some skills can not be interrupted! For example once Malfurion starts his healing ult it keeps going no matter what.

This spec functions essentially like a combination of the other two. You get dps talents to help in group while maintaining talents to push against the enemy.

On the Level 4 talent you will notice unlike the other specs Envenom was chosen. Optionally in its place you could choose Ranger's Ambush if you don't end up with many targets you think Envenom will be good against.