Mostly comes down to confidence and kindness. Realizing that these people, after high school you're probably never going to see any of them again except maybe a couple close friends and at reunions. You think you will. But different jobs or colleges, relationships, moving away... You won't. So who cares what they think? Only worry about the people who are with you forever (or could be) like significant other and any family that truly cares for you. Don't be scared to screw something up. Don't worry about lying about stuff because nobody will think you're cooler because you told that one story that one time. Confidence, because you know it doesn't matter what people think, just be yourself.

And kindness because you shouldn't take 'don't worry what others think' to mean you can be a dick to people since you won't see them later in life. Be nice to people because the cool kid who is nice is loved by most. The cool kid who's a jerk is called a douche behind his back.

My approach? Make people laugh at me instead of using others to make fun. I don't care if I look silly or stupid as long as it's good heartedly making others have a great day or even just a moment. Too much of school fun is based on putting others down or making up stories of 'being bad' which may get you cool points but no respect.