Here are some flirting pointers:
Have Confidence - Humans are great at sensing confidence (and lack of confidence). If a girl exudes confidence while flirting with me, that's half the sell.
Think Outside the Touch - We all hear about how important tactile contact is in flirtation. But a girl giving me a look along with tossing her hair, or giving me a special smile as she walked away are the flirtations I remember most. Those looks I remember were reserved for me, and I remember them more than the little touches on the arm.
Don't Overdo It - Don't be the girl who wears too much makeup. Flirt enough to let them know you're into them, but keep it subtle. Remember, though, a lot of guys don't even notice when someone is flirting with them.
Target Your Man - If you're the girl who flirts with everyone, then the guys won't think anything of it when you flirt with them. Make the person feel special by saving your flirtation for them.
Flirt With the Right Purpose - Flirting should be a little announcement that says: "Hey, I might like you." Don't do it for attention, or to make someone you like jealous. It can end up being a bad reflection on you.
Devolop Your Signature - All the famous movie stars (Marylin Monroe, Greta Garbo, etc) have their classic looks. I'm not saying you need to be a movie star, but if you can develop a signature go-to flirtation move, you'll have a comfortable move to fall back on.
Give and Take - Try to hit that perfect balance of flirting, then pulling back so the other person can flirt. It will become a little dance, and you will both find a rhythm and perhaps sparks will fly from there.
Make Sure It's Wanted - When you start flirting with someone, pay attention to their reaction. You know how horrible it is when someone awkwardly flirts with you when you're not into it. If you sense resistance, call off the dogs and live to fight another day.