Just Smile Always

If you have problems getting your feelings and opinions away from other people, learn the techniques of self-assertion, rather than using anger or avoidance by bottling them all up inside.
Take up a spiritual practice. Research shows that people who meditate have a somewhat detached approach to the problems of this life, and are calmer, happier and more contented than usual. Turning to that higher power, closing your eyes and thinking of artistic images, doing deep breathing, etc. Can give you a sense of peace.
Try to make someone else happy and you will feel happy for achieving something!
Research suggests that happy people have a simple mental strategy towards life. When they think about something good that happened to them, they explore how they personally contributed to that good feeling and feel happy about themselves.
Listen to the music that makes you feel good. When you wake up, put on some uplifting / upbeat music.
Be honest with yourself. Is there something that is keeping you from being happy - an addiction, a bad habit, or insecurity? Do something about it!
Smile! It's contagious and takes less effort than frowning. Stop stressing about money or things out of your control.
Get plenty of sleep every night.
When you receive a compliment from others, accept it and say "thank you", with a smile.
Get healthy or stay healthy by eating right and exercising.
The true key to happiness is acceptance - learning to be happy with what you already have. A lot of people know it but don't quite keep it in their minds. Never ever compare your life with that of the others. Don't be too proud, don't get envious. Accept the gifts you received and stop wishing for something 'more special'.
Pay your bills on time, and be in the habit of keeping an orderly home. Treat yourself to something special once in a while, not because you 'need' it, but just because you 'want' it. Fulfill your own desires once in a while.
Caring for and loving a pet is a great way to stay happy once you reach that goal. If you have the time, energy, and stability to take on the responsibility of caring for a pet, you might consider this. (Don't rush into this or adopt a pet for the wrong reasons! This is a long-term commitment, but is a great way to share your happiness).
Make new friends and talk to them about your problems. Listen to theirs, communicate.
Get out of your house and hang out with friends.
Even in the most terrible times, do not turn to alcohol or drugs, or anything else that is addictive, abusive to your health and others or is considered a bad habit.
Keep a "Thankful For..." Journal. Every day write down a few things that you are thankful for and then review what you have written in past entries. It's a great way to remind yourself to be thankful for what you have and to boost your mood!
Talk on the phone to a hot guy/cute girl. This makes that frown go away!
Think about happy thoughts like winning a million dollars or going to see that new movie this weekend.
Remember that things could always be a lot worse than they already are.
Remember a happy thought is a 100 times more powerful then a negative thought which is gonna make you moody