If your goal is to run in a 5K, don't just train for an imaginary race -- sign up for one. Pay attention to the calendar, though. Don't plan to run in a race that takes place next week. Give yourself enough time to train properly. The length of time depends on your starting fitness level -- in general, though, the longer you have, the better. Plan on at least a couple of months [source: Run Britain]. Once you've signed up for a race, that deadline will serve as an excellent motivator to get you outside and hitting the pavement.