I'm assuming that you talk to him a decent amount. If I assume wrong then I suggest that you start talking to him more. If I am right then, you shold find out what he likes and talk about that more. Every guy loves compliments but do it in moderation because, and I can only speak for myself and some other guys I know, a lot of guys find constant compliments to be tiring and tastless. But that's my thoughts.
When she notices you are there, and she is interested in you, that's the best flirt youc an get. It gets better though. A guy likes to be complimented with simple stuff like "You're so funny", so don't go into cheesy stuff. At least not the first time you talk to him!
To flirt you can laugh at all his jokes, make eyecontact and hold it. If he comes up to you to talk, after you look at him look down at the ground and smile slightly, almost like a smirk. Also compliment him.
It depends on the guy, different guys like different things, just like girls. Think about it. Different people have different taste.