My first build, let me know what you guys think :).

Build
1.) You want to get ambush but max expunge as soon as you can while getting Ulti when it's available.

Positioning
1.) Take Mid early game. You'll get that expunge up quickly which you can use to gank top and bottom early on.
- a fed twitch is a happy twitch

Gameplay
1.) Scout, be on the constant lookout and don't stray too far from your team.
2.) Get into position before you pop your ult. You want to hit as many heroes as you can; i can not stress this enough. If you have proper positioning, the damage, slow, crit should eat away at the heroes in no time.

Notes:
I do know that i lack life steal but the thing is, when i play twitch, i farm when i can but i mostly gank and play my role in the team fights.

Skills:
1.) Flash is for those tight situations, you can either escape or chase. A trick i often use when i am chasing a good runner is that i flash to the opponent, pop debilitating poison and finish him off.
2.) Teleport is for those situations where you're trying to push tower when everybody else is doing their own thing. Teleport to the creeps, push the tower when the time is right, destroy it, and use Ambush to escape. When used right, you can always take out a tower or two when the enemy least expects it. If the tower is at roughly half health, you can tank it and have about 25% health left.

Extra Tip
1.) With this build, you should be able to solo dragon by the time you get zeal try to do that whenever you can.