Guys are different about what they do. I, for example, am a little blunt and to the point. Some girls find it intimidating (In my experiences anyway). I'll slip a sly remark into a conversation or make sure that she catches me looking at her inappropriately or something like that. It all depends on the guy. Every guy has a different style. IMO.
Good-hearted joking. Sit near them and ask them a lot of questions. If the guy looks at you a lot when you are talking and leans in towards you that is a good sign and if he makes "accidental" contact with you a lot.