Oh, this is the hardest one so far. I have been being led to do a fast, but I admit I've been resistive. It still seems hard after reading about it, but at least now I have direction. Foster suggests starting slow. Doing 24-hour fasts (two meals). He says that most find lunch to lunch the "easiest". Do it once a week for several weeks. As you go along, God will reveal things in your life that need work. I don't completely feel ready, and I do feel like I will fail, but I really do desire to meet God on a whole new level. To seek Him more and to know Him more. The purpose of fasting is to center our thoughts and prayers firmly on Jesus Christ. But fasting will also bring about another "benefit". It will reveal what controls you. That is a sobering thought! I mean, do I really want to know? Yikes! I do want to know, and I do want to be better.
After you accomplish 24 hour fasts, and do well and feel called to "step it up" as it were, try 36 hour fast (missing 3 meals). During the 24 or 36 fasts, you can do a restrictive fast, where you abstain from food, but drink fresh fruit juice, or a normal fast, which is abstaining from food and ONLY drinking water (healthy amounts). Foster describes an absolute fast that is abstaining from all food and drink, but one should ONLY do this if he/she absolutely knows God is asking that of him/her but NEVER for more than 3 days. An absolute fast only occurred in the Bible rarely and it was clear that God supernaturally intervened.
If you feel led to go beyond a 36 hour fast, I would suggest reading Celebration of Discipline first and understand what you will be doing. Don't just jump into it. And ONLY do it to center your life on Christ. It is not a use for penance or because you think you will gain favor from God. It has to be for the right reason and the right reason is that it is God-initiated, God-ordained to center forever on God.