Hey Kid: Forgive
The single most important thing you can do to attain happiness is to forgive. I'm half-way tempted to send the blog post here... I don't know if I can add any more wisdom to that concept. It's really as simple as that statement. You can buy (and read) all of the self-help books available on "How to Find Personal Happiness" but it really all just comes down to forgiveness.
Forgiveness of yourself and forgiveness of others.
Remember this section of the Lord's Prayer: "Forgive us our trespasses as we forgive those who trespass against us." In other words, forgive me God, but only as much as I forgive those who have offended me. (Ouch.) That is our prayer. It's best we start working on our side of the bargain. Sometimes it's easy and sometimes it's difficult. I can tell you however that it gets easier the more you practice. AND... furthermore... the SOONER you start the process, the better.
Don't know where to begin? Ask God to do it for you until you can do it for yourself. He will. I know from experience. And once you realize how much better off you are, you'll learn to do it for yourself the next time. I promise.