Playing twich as an AD is too hard. But twich has the highest potential to score a pental kill in less than 5 second. So I decide to play him as a jungler. Free farming , easy to roam and gank with ambush. He can even score first blood in level 2.

http://s1096.photobucket.com/user/tienquyendahn/media/Untitled_zpst1jjcl9t.jpg.html

Pros :
Can kill everyone in 5 seconds or less after you finish your infinity edge as your third item.
CAn score many many double kill,triple kill, quadra kill and sometimes penta kill :)
Gank very easily with ambush.

Cons :
super squishy.
need good position in teamfight.

Start from golem first -> red buff -> rift scuttler -> gank if possible.

Remember that when you gank, always hit and chase. "E" if you feel that can do enough damage to score a kill

In a combat, you only have 5 seconds to decide the outcome.
That's why after playing for a longtime you will become very decisive
YOUR POSITION IS VERY IMPORTANT.MAKE SURE YOU CAN HIT THEM IN 5 SECONDs. And ALWAYS KILL THEIR AD FIRST IF POSSIBLE.
you have 3 choices:
1-Stand ON THE EDGE of teamfight.
2-Stand behind their AD .
3-Stand behind a wall

ACTIVE YOUR AMBUSH , CHOOSE A POSITION , ACTIVE YOUR ULTIMATE AND WATCH YOUR ENEMY DIE IN AN EYEBLINK. :)