One important key to consistent happiness is learning to look at situations objectively.
When someone says something that seems insulting or mean or petty, step back and think for a moment. Is that what they were really saying? If someone is staring at you in the mall, is it because you have a toilet paper tail or spinach in your teeth? Maybe it's because you're looking damn fine.
Take the time to give other possibilities a thought, before you react by being hurt, offended, nervous or embarrassed.