Most of the time, the way you dress in school decides whether you are popular or not. Check out how the cool guys in school dress and dress in a similar fashion. You can also dress differently, but appear cool. On the whole, I don't think you should even be trying to be cool, just be yourself.
I was the least popular kid in school but I had 3 good friends and I was happy!!! When you are popular you gave heaps of friend who are just there to seem cool but their not. Don't try to be the most popular just be you and have trust werthy friends!!!