I understand that it was Robert Louis Stevenson who penned this
prescription for happiness. It bears remembering and repeating.

Make up your mind to be happy. Learn to find pleasure in simple things.
Make the best of your circumstances. No one has everything, and
everyone has something of sorrow intermingled with the gladness of life.
The trick is to make the laughter outweigh the tears. Don't take yourself too seriously. 
You can't please everybody; don't let criticism worry you.
Don't let your neighbor set your standards.
Do the things you enjoy doing, but stay out of debt.
Don't borrow trouble. Imaginary things are harder to bear than the actual ones.
Since hate poisons the soul, do not cherish enmities and grudges.
Don't hold post-mortems. Don't spend your life brooding over sorrows and mistakes. 
Don't be one who never gets over things.
Do what you can for those less fortunate than yourself.
Keep busy at something. A very busy person never has time to be unhappy.