Okay since you are 20 years old then you are most likely in the transition period that a lot of girls find it hard to get out of. I think that you are also in that period of your life where you are obviously looking for something more out a relationship (boyfriend, friends) but there is really nothing you should be doing but being yourself to get the attention. I am sure that there are other girls around you that are a little less than modest around boys and boys at that age are really just dumb enough to follow that route. I have been one of those girls that have always had more friends that were boys than girls because I relate to boys better. If you are really looking to make more friends (boys or otherwise) then you need to be yourself but you can also put yourself out there and try making new friends... Try talking to someone that you don't know or someone that you would be unlikely to talk to on a normal basis. Good luck!
A lot of guys like a girl with confidence, though even if your not confident you can fake it. As the saying goes to "fake it til you make it". Have fun with female friends and go out with groups(guys and girls). Be yourself, and don't be outwardly looking for attention too much. Please don't lower yourself to start dressing in tiny clothing. You might get attention that way, but trust me it's not the attention you want. I grew up with brothers, so I feel more comfortable around them than catty girls, since you can just play sports without all the gossiping. Try joining a club or sport, something you enjoy where you can meet more guys, and girls. good luck.
just be yourself duck, dont try pretend to be something you arent just to impress a guy, just start a conversation with them, say hi ask they are, theres someone for everyone