Not Updated For Current Season
Early game: Try to lane with a tanky character like rammus, it's even better if he has some kind of a taunt to help you get ur shots in. The reason you're starting with expunge instead of ambush like most twitches do is that you really got to understand that you will be killed in a matter of seconds when they turn to focus you. Let the tanky one attack first so you can get a couple of shots in and blow em up with ur godlike ability.
Mid-game: You can start using ambush to go on gank-duty. With ur bloodthirster most likely finished by now and berserker greaves at ur speedy disposal, you should be able to help close down midlane (this is taken into consideration of you not being in mid, you'll have to go with a different approach). You won't be in such high need of those speedlike items with the combination of ur ambush and shoes (and ulti if you need it). If the enemy has an oracle without you knowing it you can easly exhaust him, put on ignite and rain hell on his ***.
End/late-game: This all comes down to how you've been doing earlier this game! You will have to coop with your team more than you have been doing throught the game and be rather careful since some on the opposing team might have quite high burst dps! Twitch is really squishy and can easly be blown away by bursts of annie and malzahar. Suppress these early and don't be the one to engage (duh!). If you've been able to execute this build and playstyle good enough the enemy-team will most likely have some oracles and wards running around, so inspect them before jumping them. Have gotten a easy quad kill with only ulti as they tried to down a tower with me alone, so with this damage it should be a breeze. (can get frozen mallet if they target you alot!)
Comment and rate as this is my first guide!