Most Helpful Guy
What you're doing wrong is cold approaching and failing to take hints.
When you cold approach a girl, you have no idea what you're dealing with. She may NOT be looking for a random guy to get acquainted with. Infact, if she's with a group of friends it's a hard case because ... the club is loud and you can't hear each other, you have her friends to deal with (therefore you have to win the crowd first to be accepted, otherwise they'll c0ckblock you), and then there's competition at hand. If there's other good-looking guys present, then you got competition to beat. And no matter what you do, she'll want a sexier buff stud way before you.
One-night stands, or quick sex is easy for guys who are in good shape, wear decent clothing, and just have a pretty face. Physical attraction = easy sex.
So if you hope to change this around, get in the gym and tone up your muscles. Wear a good outfit. You'll notice the female attention picking up, and that's when you know you can get away with taking a girl home. Girls generally don't say sh*t to a guy, but instead they'll give off signals of interest. Such as proximity (getting close to the guy), eye contact, hair brushing, or generally turning their bodies your way to face you. Just study some body language tips.
Instead of any cold approaching, you can pay attention to the females around your area and spot their signals of interest. And play it cool with them. If you seriously want sex, spend a few minutes talking to her and then put it on the table and say you find her very attractive and want her to come home with you right now.