I've blogged about this before, but I think it's time to mention it again: there is nothing that helps your productivity like a break. Have you taken a break lately?
Don't just take a break, but take some time to go for a walk, go for a bike ride, or spend some time on a treadmill. The exercise will loosen you up a little, help to reduce stress, improve your outlook on life, and improve how well you sleep at night.
A break gets your mind off of work for a little while and lets you focus on something else. If you're like me and your passion IS your business, then you need to find something else to do. I read; I know others who paint or go to the park with their dog.
While the temptation for successful business owners is to spend 24/7 in front of the computer, you will actually be MORE effective if you take some time away from the computer and return to it refreshed.