I think happiness is no different than fitness or health...you have to work on it and it becomes better.
Some days I am just happy because I think its in my nature. In any situation, I always end up looking at it from some kind of positive angle.
Other times I listen to music I like or look at photos or videos of my daughter and that will get me REALLY happy.
Some days I start out happy...like today....and end up in a funk because of something some one else did that I allowed to steal my sunshine.
So identify things that make you feel happy and then keep them close by for when you need a boost.