Productivity blog Zen Habits has a good article on how to make your day better, including this little gem: no matter how stressed you are, if you can get just one important thing done, you'll have had a successful day.
When I say important, I mean things that will have a huge impact on your life (personally or career wise) over the long run. Not things that need to be done today or else. Here's why: If you get something important done, something that will help you in the long run (even if it's only a step towards a major accomplishment, it's important), you will feel great! You'll feel a sense of accomplishment. That makes any day a great day.
What's your "important thing"? Thoughts in the comments.