- Don't hold grudges. If it's about something you can't resolve you can either let IT go, or let the relationship go. Nothing is worse than letting jerks live rent free in your head.
- Travel. Even if it is in your own backyard. Go somewhere new. try some food you haven't tried. Go be a tourist unashamedly.
- Say yes to opportunity. It's easier to say no to things that are slightly (or hugely) new and a little scary.
- Say no to things that make you unhappy. Don't make lame excuses, just politely but firmly decline.
- Walk somewhere. Go look at trees and flowers or even other people at least once in a while.
- Do something nice for someone else. Hold a door, buy some flowers, pay for the guy behind you in lines coffee.
- Have a pet. Even a fish or plant Talk to them. Give some love, get some love.
- Have a hobby. Collect stamps, knit, do Sudoku, do something you enjoy every day.
- Make something by hand. Doesn't matter how small, make it with your own digits.
- Walk around with a smile on your face. A positive outlook becomes a habit when you do this. Try not to look too deranged. A small Buddhist half smile is a good start.
Fake it until you make it.
These are of course only as helpful as you want them to be. Your mileage may vary.