To fast, try to stay away from sugar, white flour products a day or more ahead of time..they make you want more.
Use the amino acid L-glutamine...helps me w/ carb cravings and helps me when I fast.
Drink LOTS of water, and/or juice. Anytime you start to get hungry, go drink a glass or two. I've done juice fasts, one water fast, made it through 3 day fasts and one five day fast!
The first and second evenings are toughest for me.