Lie on your back, and lift the bar up as if you were going to bench press; this will add an extra challenge as well as a bit of shoulder work to the exercise. People who are new to weight-lifting should try this exercise with a lighter, more comfortable weight or with the bar only. You want these to add more weight to your back as you lift your legs; you shouldn't rock when doing the exercise. If you have trouble keeping your arms steady during this exercise, opt for a lighter weight.
Keep your arms steady. Tighten your abs and lift your heels from the ground. Lift your legs toward the bar to the right of your right hand, keeping your lower back against the floor the whole time.
Lower your legs back down to the starting position, but do not let your heels touch the ground. Then lift your legs toward the bar to the left of your left hand, again, keeping your lower back against the floor. Then slowly lower your legs again to the starting position. This is one repetition.
Repeat. To do a full "300" Workout, the exercise should be repeated 50 times, but beginners should be cautious and use their best judgment about how many repetitions they can do. You can always build up to the 50 reps as you build more muscle.