Hang around positive people, do positive things. Volunteer at a nursing home, hospital, shelter or even a rehab. Helping a person---- and the self satisfaction that comes from doing so, is a feeling you won't soon forget. (either will the person you have helped, and expected nothing in return)
I just read about a study in exactly this topic. This is what makes people the happiest: having all your primary relationships in good shape. So if you are getting along with your family, friends, teachers, boss, etc. your feeling of well-being will be consistently elevated.
Stop yearning to be like others or want what they have. Stop yearning for material things. Stop thinking that you need to look like someone on TV or some photo-shopped model in a magazine or ad. Stop striving to buy the next big thing because everyone else has one.
Learn to love the things you have, the things you can change, the things that are uniquely you. Only YOU can make YOU happy.