I'm thinkin' Hayabusarider and 0sully probably have more success with women than the other folks in this thread.
My tips: Be confident and lighthearted.
Confident: none of this, "well, uh, I was wondering, um, if you, well, if you're not too busy or anything, might want to sometime, you know..." Sigh. What you want to say is: "Can I take you to dinner Friday night?"
Yes, it's hard as hell to say. Gals, you have no idea how hard that is. But guys, girls respect it.
Lighthearted: If she says no, it's not the end of the world. Don't think for a moment that it's the end of the world, and walk away smiling, looking for the next girl you can ask out.