Think deeply grateful thoughts for the things you have. This is a very effective way to become more happy. If you feel grateful for the things you have, you appreciate what you have and feel more satisfied with your life.
View the glass as half-full instead of half-empty. Your girlfriend/ boyfriend broke up with you? Now you have the chance to meet someone good for you! You lost your job? Now you can seize the opportunity to find a better one! Adjust your mentality so that, in each thing that happens, you see some kernel of good, and say hopeful words, "It will be all right!", or "It's going to be good.", or "I'll keep expecting good results."
Put yourself in situations where fortunate things are likely to be achieved or happen where preparation meets opportunity. It's easier to remain optimistic, if you set yourself up for success. Cheating on a partner, or stealing someone's bicycle — while temporarily thrilling — rarely ends well for any party involved. Ask yourself before you act out: Am I setting myself up for success or for failure?