I want to establish that a happy life is a matter of choice. A happy life is not one lived in El-dorado. Neither is it a perfect life.
Once you have fulfilled the premise of deciding to be happy. You must ensure some tenets to sustain it:-
Observe the golden rule : do unto others as you will have them do to you. This equally takes care of the third law of motion, in effect what eversion you sow you will reap. And equally reduces bad effects of some karma.
Express unbiased love . Avoid any form of wickedness it is absolutely useless, you will hurt yourself and eventually rob you of a happy life.
As much as you can be kind.
Live within your means. Modesty should be pursued almost zealously.
Learn to be spiritual, as it curtails vanity that propagates anxiety. At least some form of meditation will be nice. You can try heartfulness meditation if you have no idea.
Have a purpose driven life, live for something that is goal oriented , especially for the benefits of mankind, in the long run and not necessarily for self aggradizement . But understand that some unanswered prayers are also answers sometimes.
It is a tough world, but avoid stress as much as you can. Take care of you, no one can do it better. Some form of self love is essential for preservation. Love yourself, narcissism is relative but do not be carried away. Living for others remains noble and the ultimate service.
Do not compare yourself to others and expect less from people but wish them well all the time.
In each situation make the best out of it, and learn to accept responsibilities. Blaming others have never transmuted to stardom. Learn to forgive , forgetting can be handled later.
Take time to be a child, laugh at your self, play, dance, have faith without borders as children do. Believe in miracles. Only those who do will experience it.