One of my co-workers posted this article (available here) in his cubicle and it has slowly spread around the office. In my vicinity alone, I can count three other co-workers hanging it in their cublicle—including me.
I find all of the tips important and easy to remember, but a few are particular stand outs: I am just as capable as my co-worker. No one gets up in the morning wanting to have a bad day. Fixing a process is a million times easier than fixing a person. Honor the other 15 hours a person spends away from the office. Manage your own happiness.
The power to be happy at work is within your control. It is entirely up to you whether or not you leave as happy as you did when you arrived.