I failed a number of times myself. I would start off good and then just give into food before the day was over. I have started another fast. Right now I am on day 6, and after going that long without food I wouldn't dare give in now.
What worked for me was a pre-fast diet a week before i started fasting. I choose pineapple chunks in a can in pineapple juice, vanilla greek yogurt and very little tuna. I did this for a week and exercised almost every day. I lost 9 pounds in one week. I wasn't even hungy becasue pineapple not only burns fat but it works as a natural appetite suppresent. With the motivation of losing 9 pounds it was very easy to start the fast.
So try chosing a pre-fast plan that will work for you for a week or longer if needed. Either a Juice fast or fruit and veggie fast. Try to get as much exercise in as you can...as this will increase dopamine in the brain and help you resist the temptation to cheat!