Prone to procrastination? Try entering "Not to Do" items into your regular to-do list, where you can see them regularly. These might include "don't play solitaire" or "don't surf the sports scores." If you go through the day without doing these things, check them off your list—and it'll be that much easier to forgo them tomorrow.
Or you can tell yourself not to do tasks today that you should do tomorrow, after you've finished more important tasks. This can keep you from procrastinating on big projects by tackling easier but less crucial assignments. Once you've done your more important work, change those don'ts to do's and finish those easier tasks.