Of course, being happy at work depends mostly on how much you like your job. But there are also smaller steps that can boost your happiness, as well. Some of these steps are VERY small, but the fact that you're taking steps to improve your situation itself boosts happiness.
1. Check for eyestrain by putting your hand to your forehead in a salute. If your eyes feel relieved, your work space is too bright.
2. Sit up straight with your shoulders down -- every time I adjust my sitting position, I instantly feel more energetic and cheerier.
3. Get a phone headset. I resisted for a long time, because it looks so preposterous, but it's really much more comfortable. Also, it lets me pace while I talk on the phone, which also looks preposterous, but is energizing.
4. Don't keep candy on your desk. Studies show that people are much more likely to snack when a treat is within easy reach, and a handful of M&Ms each day could mean a weight gain of five pounds by year's end.
5. Never say "yes" on the phone; instead, say, "I'll get back to you." When you're actually speaking to someone, the desire to be accommodating is very strong, and can lead you to say "yes" without enough consideration. Along the same lines...
6. When deciding whether to say "yes," imagine that you're accepting a job that you'll have to do next week. Don't agree to something just because it seems so far off that it doesn't seem onerous.
7. Don't let yourself get too hungry. The Big Man goes without eating for hours and hours at a time, so once, trying to be helpful, I bought him a big bag of granola to keep in his desk. He ate the whole bag in one day and ended up sick as a dog. Lesson: eat regularly.
8. Take care of difficult calls, tasks, or emails as quickly as possible. Procrastinating makes them harder; getting them done gives a big boost of relieved energy.
9. If you're feeling overwhelmed, think hard about how you spend your time. Be honest. How much time do you spend surfing the internet, looking for things you've misplaced, or doing a task that's really someone else's job? Also...
10. Let yourself stay ignorant of things you don't need to know.
11. Go outside at least once a day, and if possible, take a walk. The sunlight and activity is good for your focus, mood, and retention of information.
12. Say "Good morning" to everyone. Social contact is cheering, and if you feel that you're on good terms with all the people in your office, you'll be happier each day. Also, it's polite.