Confidence.
Don't be arrogant or prudent in your actions.
How can I become popular?
I agree with Tannis Mitchell, "There's no such thing as being popular,"
Popularity is about being yourself, if you want people to like you, they might as well like the real you. Don't forget there will be those who won't like you, just let them be and don't sink to their level.
If you're referring to the people who have lots of friends and everyone knows them, those people are called "outgoing" like Tannis said. If you want to be outgoing, I know many people do, then it's all about confidence like Nick Major said.
Good luck! And don't forget, popularity is just a stereotype.
Well, there's no such thing as being popular, but people who have the most friend's are often very out going, and just accept's people for who they are, and has everything out for themselves. People want to be this person, and they often are very funny and very attractive.