I see people almost daily who make an effort at trying to be cool. When you do that, it has the opposite effect. It just makes you look desperate.
The best way to be cool is to just be yourself without worrying about what others think of you. People will notice the confidence that you have in yourself and that you're happy with who you are and they've got to respect it. (Inspired by an arrogant jackass that I had to deal with today) Don't try to be what you think other people like.