Loki and Dee gave great descriptions.. maintain eye contact! and watch his. nothing says "I'm not interested" more than your partner in conversation looking around the room as your speaking. And, ask him questions. It shows your interested AND gives you the ability to continue the conversation without akward silences, and allows you both to see what you may have in common. Best of Luck!
Teasing tends to get the fastest results, if the feeling is mutual. In my conversations with guys, the most attractive kind of flirting is a kind of physical confidence. Lots of steady eye contact, lots of smiling, body turned towards them and 'open', i.e. arms not crossed over the chest, turned away or hunched - makes it look like you're defensive or shutting them out. A willingness to talk to them like you know them well, and able to have a good laugh even if it's at your own expense. It will get the attention of most people in the same room which increases the interest as well, because suddenly everyone feels they have to compete to get you.