A good guide to fasting and praying is "God's Chosen Fast: A Spiritual and Practical Guide to Fasting" by Arthur Wallis. As of November 2015, this book has received a rating of 4.5 stars out of 5 based on 23 customer reviews on Amazon.
"God's Chosen Fast" is a biblical study of fasting. It gives an extensive account of the numerous instances the Bible talks about fasting, from both the Old Testament and the New. In this book are teachings on what happens to the body and the spirit during fasting, advice on when fasting is discouraged, and a guide on how to "break" a fast properly. Mr. Wallis also included a diary of a 21-day fast.