If you've ever been to a gym in January, you'll see the crowds of people pouring in to work out, but come back in March and you can bet most of those people will be gone. As this illustrates, motivation is the most important factor in sticking to your workout routine, but it can be the hardest to keep up. Follow these simple and enjoyable tips on how to stay motivated when you work out.

Stick with a plan. If you make working out part of your daily schedule, it will be much easier to keep up with. Once you do something every day for two to three weeks, it becomes an ingrained habit, like brushing your teeth. Many people like to work out in the mornings because you're less likely to make excuses like being tired from work, hungry or too busy. Of course it's not easy getting up earlier, but think about those rock hard abs you want, the jiggle-free arms or looking hot on the beach.

Set your sights on success. Practice mantras when you work out. These can be especially helpful when you're doing something repetitive. When you're on the treadmill, for instance, every time you start thinking "I can't" or "I'm too tired," make a conscious effort to replace these thoughts with "I can and I will" or "I feel strong." It may seem corny or unnatural at first, but these simple phrases actually work. Repeating something enough will place it in your subconscious, which will register it as fact. And pretty soon the mantras become reality.

Write your way to success. Write out your fitness goals and keep a record of your workouts each day. You can use Excel sheets or whatever suits you, from notes to tally marks to crossing off a calendar. Set realistic but challenging goals and reward yourself when you accomplish each one. When you accomplish major milestones, buy yourself a new pair of training sneakers or get that new CD you wanted.

Play mind games. Display pictures of yourself at your goal weight or hang up pictures of your favorite athletes or fit models to motivate you. Don't pick photos of unhealthily thin people because that will defeat the purpose and only make you feel worse. Make a collage with motivated words and pictures of champions or star athletes. Looking at this before you work out can be very motivating.

Be a star. Create your own soundtrack to work out with and imagine you are starring in a "Rocky" type movie. Make yourself your own hero. Congratulate yourself every day on defeating your own worst enemy -- your negative thoughts.