How to make keep the guy you are flirting with.

Touch him like you didn't intend to. 
(give him a good reaction or grab his arm acting like you are falling off)

Have a casual drink together and show you are a little tipsy. (show that you are not perfect, make him want to protect you!)

Wear something different. (if you have never been sexy in front of him, its time to show that you can be sexy too)

When you're with him, try to show that there are other guys in the picture as well. (Not too much though, just enough so he gets jealous)

Stare at him. When you have eye contact, smile. (He will melt)