Flirting is weird. In my experience, it's all about confidence. Too little confidence, and you can come across as creepy (or that's how it was with me... I'm quiet, so I'd kinda lurk rather than flirt... creeepy!). Too much, and you're an ass (I only know this from watching others).
Flirting can be crazy subtle... I've never been overt, but here's some things that worked for me. Smile if she looks your way. Watch her eyes when you talk to her, but glance at her mouth from time to time. When other people say things, funny or serious, look at her reaction. If you accidentally (do not fake an accident, that's creeper territory) touch her, overreact a little bit (she'll know you're thinking about her personal space, and if you're awkward like me, that's a "tell"). Compliment her on something other than her personal appearance. Try to make her laugh or smile, try too hard if she's looking down.
All that subtlety is for nothing sometimes... I got my wife's attention by sarcastically talking about how damned sexy I was. She thought I was flirting, I thought I was being silly and self-deprecating.