I'm a bit older and married, but if a guy approached me too directly when I was single, I'd pretty much always turn him down. (There were guys I would have made exceptions for, like Spike on BtVS., just not real live living guys.) Back then, I was thin and pretty, and I got hit on all the time, usually by guys who were pretty obviously looking at my boobs and didn't seem to have any interest in having an actual conversation with me.
What worked much better to get my attention was if a guy initiated a conversation about something I was interested in. Like if I was wearing an Einstuerzende Neubauten shirt and a guy asked me what was my favorite song on Haus der Luge, and what I thought the white stuff on the cover was supposed to be. The more obscure, the better. If I was reading a book and he had read it, big time bonus points. If I was drawing and he actually showed more interest in my art than my boobs, that was great.
If I liked a guy, I'd find reasons to talk to him or at least be near him, and I'd smile at him and make eye contact. Also, I'd be more likely to wear something that drew attention to my boobs or my legs, and I'd position myself to give him a good view. Guys like boobs, even smart guys. I just had to know they were smart before I wanted them to notice my boobs.