One of the best things you can do is keep a fitness log. Nothing elaborate or time-consuming, mind you -- just a simple, written record of your workouts.

After working out, write down everything you did. For cardio workouts, write down the amount of time you spent working out and how intense a workout it was. For strength training, note the amount of weight and number of repetitions for each exercise. By keeping track of your workouts, you'll see your progress more readily-and find it easier to stick to your fitness plan.