When it's time to work out, even if you don't feel like it, go ahead and get changed. Many times, once you've done that you'll go ahead and do the workout.
Set goals for working out and then reward yourself for them - but not junk food or sweets though! So maybe for every 15 workouts you do you buy yourself a new CD, or something to wear. Or maybe if you lose 5 pounds you'll go see a show you've been wanting to see.
And finally, if you miss a day, don't use that as a reason to quit - just get back into the program the next day.
There's no magic formula to working out regularly, it's simply a case of doing the little things right day after day. So why not make today the day that it all starts for you?