Some people just try too hard. They deliver cheesy pick up lines, show off the muscle they wish they had, and all around act like idiots.
You want to be a good flirt? It's actually suprisingly easy.
Women (at least in my experience) love a few things. They love a man who can get dressed well, but still has a little bit of an edgier side to him. They love a man who is confident in himself, and expresses that in friendly ways (approaching them, starting conversation, etc).
Confidence is key. Style is also key.
Don't walk into a dive bar wearing a suit, but don't walk into a five star eatery in jeans. Don't talk about how cool you are, or how well you're doing for yourself. Ask he engaging questions and LISTEN to what she has to say. Make her feel like she's the only woman in the room. Even if
Megan Fox and Jenna Jameson walk past you and wink, pay them no attention. Keep focused on the person you're making conversation with. A sense of humor works wonders when the situation gets awkward.
Lets recap:
Be stylish.
Be engaging.
Be confident.
Charisma is very hard to teach, unfortunately.