Happiness is just another state of mind; like sad, lonely, hungry, angry, etc. If given a choice, which would, you choose? Well, the good news is...you do have a choice and it is up to you which ever state you are in. It is your thoughts which decide what state you are in, so if you want to change your state; change your thoughts! It isn't always easy, but you can do it. Ask yourself throughout the day "How am I feeling?" Then ask, "Why am I feeling this?" then, "What am I thinking?" and finally, "What thought would serve me to feel best right now?" You want to peel through the layers with whatever questions work best for you, but mainly find the source of your thoughts and feelings, be aware of them, and then correct them to what is to your advantage at the given time.
Controlling your thoughts is really the key to happiness. If you don't, they are sure to control you. Considering the "Laws of Attraction" what you think about, you bring about. Your thoughts are powerful magnets attracting to you the things you think about most. This is a proven fact of life and knowing this should help you figure out why you are in the situation you're already in. "What have you been thinking about lately?" I remember when I first discovered this, I could see clearly how many negative thoughts I was thinking and could easily understand why things were not going well for me. For example, I would leave my house thinking "the bus will probably be late again" and it would! Everyday... I always had to take cabs. Now when I leave I allow myself plenty of time and say things like "I never have to wait long for a bus." And I never do. I catch them all right away now. This works so much better for me.
Now that you are in control of your thoughts, why not only think happy ones? It is impossible for you to feel bad when having good thoughts. This has also been scientifically proven. Think back to a time when you laughed so hard you were in tears. If you really focus you should be able to come up with several of them. Hold those images in your mind as long as possible. Then whenever you want to change your thoughts, one of them will appear in your mind and you can't help but smile at the very least. Along with that you will want to remember to keep good thoughts as much as possible. I have found several products to be useful as positive affirmations to keep you in check. The more good thoughts you have the more good you are bringing into your life and happy thoughts create more happy thoughts, and so on. This has a snowball effect. Soon it takes off automatically and turns into a giant boulder of good thoughts and good times!