Think more positively. The easiest way to become happier is to make an effort to be a more optimistic person. You may think that some people are more negative than others, but this is lazy thinking that can keep you from being happier than you are today. Your personal situation may not be in your control, but you can always control your perspective, and making the effort to look at the bright side of any situation instead of focusing on all of the negative aspects you see will make you be a happier person.
To think more positively, you have to be ready to monitor your own thoughts. Notice when negative thoughts are creeping up and fight them with positive thoughts – and logic. How many of your negative thoughts are just a part of “worst case scenario” thinking or of your insistence on expecting the worst in any situation?
An easy way to think more positively is to hang around more positive people. Their optimistic energy will rub off on you.