What can i say? farm minions dont be too aggressive til your first BF sword and then once you have it melt the enemy team like hot knife in butter. with my build the only reason you'll need stealth is attack speed (and positioning but my point is oracles won't be very effective). Twitch can completely desimate teams and i even have record of getting triple afterlife kill from poison and then after that I almost got penta if the bloody support hadn't gone and stole 2 of my kills with that starfall ability.

With this build you may be burning away your mana in which case you gotta get blue buff as much as you can (i tend to spend 80% of my mana on stealth for the attack speed bonus and the rest on slowing and killing the champions that "escaped")

Ahh farming the fields the fresh air full of the smell of cow poo.... but not in League.... farming is the most important thing for twitch early game if he's going to be able to afford his items he needs to be able to afford first bf sword by level 5 preferably level 7 at the latest.

Pros:
Tons of kills
STEALTH!
easy and fast farming
POISON!
imba slow
HE'S I ******** RAT!
long range and impale style ulti (attacks go through enemies)
Enemy hates you.
can take out entire enemy team in 2-6 shots
Cons:
Poison sometimes steals kills
Squishy til warmogs
almost always focused target

Twitch is (contrary to popular belief) good in the middle. but he is usually forced into the bottom lane in which case you will want a support to be in lane with you. the best of these are:
Taric; (he has heal stun and a buff that also helps with damage)
Soraka; (she has 2 heals can silence the enemy and give you mana on top of which has an aoe that makes expunge even more deadly)
Alistar; (if you need to know why alistar is the best ever support to help twitch you are playing the wrong game. but to explain it's because he has the ability to set up free kills AND heal you AND he doesn't die AND he stuns AND he looks sooo cool)