You just stop for a sec. Happiness is a choice, really. (Wish it was the choice I mad when I was feeling depressed). Happiness is stopping to smell the tulips and not just the roses! Sometimes I just look around and think of how small I am, and look at things like cars driving and it feels so surreal. People had to think of those cars. Or I look at a tree and think, "I wonder how many people and how many stories have walked past this tree". Just see the beauty in everything that occurs. Even the bad things! I have things I could choose to resent in my life but, really, I think I've had a 'perfect life' - just an unconventional one! It's made me a great person, in my humble opinion

Also, aim to do no harm! If you are peaceful with other things, you will be peaceful with yourself. If you can feel peace, you can feel happiness. I mean no harm in explicit terms. Don't swat a fly, kill a spider, or be sarcastic with a stranger talking to you who might be nervous. When I'm being HappyBrenden, that's how.
(And also don't be TOO self-critical! Accept yourself for who you are, whilst never settling)