I fast pretty regularly. I would say, about once a month or so. Now, by fasting, I mean a juice fast, which is to abstain from eating solid foods, and only have fresh fruit and vegetable juices and water. With the Gracie diet, I know there are plenty of juice combinations I can follow. If I'm not being too strict with the fast, I can follow the recipes from the Juicing Bible. If your curious about the proper way to do a fast, and how to come off of a fast, then i recommend reading Juice Fasting and Detoxification. Keep in mind that this book does not contain any recipes, it is strictly a guideline book.
So, to kick off the fast I have planned for this week, I intend to do something a little different. I will use Shakeology for my fast. So, for one of the juice concoctions I will follow the Shakeology recipes. I will also kick it off with a salt water flush. The mixture I use for this is 1 quart (thats 4 cups), and 1 teaspoon of sea salt (not table salt, as this contains iodide). The site linked said use 2 teaspoons, so try both and see which ones work for you.
From experience, I already know that the first day I won't feel a thing. By Day 2 I get "hyper-focus" as everything gets really clear, and by the end of Day 2 I get really bad headaches, and by Day 3 all I can think about is food. After Day 3, its easy sailing. But those are my results, and your mileage may vary.