Often what a school needs to become a happy place is for everyone--students and adults--to treat each other better.
Treat everyone with respect--fellow students, faculty, administrators. Help keep your school clean--if you walk along and see a gum wrapper on the floor, pick it up and throw it out. Acknowledge people. If you see someone you know, smile and say hello. If you pass a teacher you don't know, at least smile. Include more people in your group of friends. See if another student looks as if s/he is left out--at least introduce yourself and talk to him/her. You don't have to be friends, but be nice.Recognize that no one is beneath anyone else. Smile and say hello to the cleaning people as well as the people who work in the cafeteria.If a student says something hurtful or mean about another student, tell them that is not a good thing to say. It's difficult, but you can tell them that that kind of language makes you uncomfortable.Thank your teacher as you leave class. They have put a lot of effort into preparing the lesson.
Improving a school often means improving the atmosphere between students and students and students and adults. It is not hard for an individual to do, but it requires vigilance. If more students act this way, the school gradually, and then more quickly, gets happier.
Hope this helps:)