Im just not that into you.

Ladies AND gents I ask you this simple but very complex question. How does one know when another of a different sex is intrested in you? How do you convey that you are into them without seeming like another jack-off. Many people will just tell you its all about the individual person but I tell you that's b.s because there are some people who can get many many partners just because they know the "right thing to say" and some people can't get a break at all. They are "just friends' with whoever they meet. Is it a manner of how agressive you are to get that partner? I have seen many good looking guys get turned down by girls and some downright ugly guys get a crazy ammount of girls. Vice versa as well. I have encountered this problem recently. I am a bit shy but at the same time I want to know if the girl is into me and want to show her im into her. Lets get your opinion mibbbbbbbba.