A pre-cleanse is best, especially if you're full of refined sugars (I speak from EXPERIENCE). Take 5-7 days and cut out all sugars, yeast, and caffeine. Then maybe your willpower will be able to translate into action. Once you make it past the first 3 or 4 days it gets loads easier.
But like I told the other poster above, you have to decide what you want to do the most - eat or fast. Once you've made the mental decision to do it, then like Nike says, "Just DO IT." :^) God bless!