Avoid doing these if you want to be happy :
1. Living in the past
The past is over, there's nothing you can do about it anymore. Move on. Bring along the lessons you learned from your past to the future, instead of dwelling on it constantly.
2. Comparing yourself to others
You are who you are. You are not someone else. Don't compare yourself to others, the only person that you could be better than is the person you were yesterday. You will only set back your own personal progress if you remain fixated on others' progress.
3. Involving yourself in drama
There's no reason for you to butt into someone else's business. I'm sure you'd be pissed off if someone did it to you. Try not to involve yourself in stuffs that are completely irrelevant to your life.
4. Having pessimistic thoughts/tendencies
Seeing the glass half empty is a terrible way to go about life. The saying - "If we all threw our problems in a pile and saw everyone else's, we'd grab ours back." exists for a reason.
5. Over criticizing yourself
No doubt, self-reflection is a good tool in life. But that's a different meaning when you constantly put yourself down. Think positively, open up your mind, focus on improving yourself rather than hating on yourself.
Despite what many would believe, it's always not too late to seek and bring happiness into your life. Achieving happiness isn't a one step process, and the feat sure isn't easy either.