This is by far the best Fasting resource I have seen on the net so far:
www.freedomyou.com/level%20...Guide.htm

Don't let the religious slant put you off.
If you're not Christian, I would suggest that you substitute your own spiritual terminology for the Christian stuff -- as the rest of the info is very accurate and valuable, and the spiritual intentions are all good.

As with all health info though, I would recommend not relying on this exclusively. It's a good idea to round out your knowledge with several sources.