It all comes down to wanting it bad enough. The next time some junk food arrives in front of you, ask yourself "Do I want to eat this trash and be satisfied for the next 10 minutes? Or should I avoid this and be satisfied with a fit body for a LOT longer?"
Rinse and repeat.
Also, check out the stickies for the quality information. IMO, information is 20% of the battle, and the rest is discipline/effort.