DIET DIET DIET. You have to watch what you eat...no crap! You HAVE to eat every 3 hours...4 at the most but don't wait that long unless you have to! Make sure you eat a protein with evry meal and snack. You must get 5-6 days of cardio in and you HAVE to strength train. If you don't pick up the weights, your body will burn off muscle during your cardio sessions. Eating every few hours keeps your body from canabalizing as well.
I highly recommend the e-book "Burn the Fat Feed the Muscle" by Tom Venuto. Amazing read, very easy to follow, principals are excellent and healthy. I have been following the plan for almost 8 weeks and I am seeing positive results every week (every week I don't cheat, that is).