Two main things.
1: You need to kite the jungle creeps. Krugs will probably be a no-go for Twitch until late. He doesn't have the tankiness to deal with creeps without kiting them. This feeds into...
2: Gank constantly. I used to play Jungle Twitch, and the key is to gank a LOT. Ambush is a very potent ganking tool. Use it to sneak into the lane and get the drop on your foe.
Start with Ambush at level 1 and use the bonus Attack Speed to clear your first camp. Ask for a good leash, and start with Red. Put a point in Contaminate and immediately go mid. With Red slow, Ambush Attack Speed, and Contaminate/Deadly Venom damage, you'll almost always force Flash. Take that victory and do the Scuttle Crabs before coming back and ganking again. Do Blue when you can, but you'll probably have to back afterwards unless you kite it REALLY well.