Sexual Relationships 
Sexual Health 
This isn't about being romantic or self confident, but ideas on what you can actually say! My biggest suggestion, is to start by talking about casual topics until you get her information. Then, you can talk more and...not just magically bring up sex, but just bring it up more often. So for talking to girls, like cold approaching in public...
So, the way that you talk casually, is to just find a random and cool topic! Like let's say you walk up to her and she's reading a book. You could say it's rare to find people who <3 reading books still, and that you love the fiction or whatever book but what's she reading since you're curious? Or if she's on her phone, you could mention the Pokemon Go craze and ask her if she plays or does she like it and debate about that. After you talk for a while, you can ask her or suggest that she find you on Twitter, KIK, etc, and so you guys can talk about this stuff more. But DON'T make it seem like you're looking for sex even remotely, not till after you're friends and regularly talking. Otherwise she'll be suspicious and shoot you down anyway.
My next main tip to guys is that after the initial conversation make it clear to her, that you want her sexually. Even if it's only subtle flirting. Like you could makes jokes about sex or her (subtle and still fairly polite jokes!), ask her about her friends or boyfriend to make sure she's single...show some kind of interest!
If you want her to be interested back, you'll have to be interesting to her too. Which is why the casual conversation idea works so well. Most guys in public approach girls solely to ask them out. But you just find a common interest, and then you walk away and when you talk later you're still only a friend? That can be really interesting and almost rare. Even if you include sexual things a little, the fact that you're not going all out with it tells her you actually put effort in, and then she'll want to keep talking to you!
If you're in a bar/club looking for a hookup, then things can either be easier or way worse for you. On one hand, she'll be looking to sleep with a guy probably too. On the other hand lots of girls go to bars with their friends, and she'll be surrounded by other girls! So, lots of guys may hate this advice but I would suggest to stop going for the super and social hot girls. Go for the girls that are only with a friend or two, or even are alone! They may even be shy...but go for girls who will actually take the time to talk to you instead of blowing you off. Once you get more experience things should go more easily for you.
I would also say that it'd probably would be best for guys to stop cold approaching the old fashioned way. If you haven't built up a comfort level with her, there's a 99% chance you'll get shot down. After all, why are you cold approaching? Because you think she's hot! And she knows, so to her that's like you're asking for sex. So if you become even just a casual friend first, then things should be way easier for you.
Hope these tips help!
Most Helpful Guy