Some of you may know Charlie Handren as the guy in charge of the prayer ministry at several past DG conferences. He is also Bethlehem Baptist's Church Planting Resident and will be going out to start a new church in a few months. He preached this weekend while Piper is in Portland.
His sermon was on John 15:1-11. One of his points was that the word "ask" in the phrase "ask whatever you wish, and it will be done for you" implies fervency. To put this passion for prayer in practice, he led his small group (the nucleus of the new church) on a 40 day fast from February 27 to April 7. Each day he blogged a short devotional on this passage in John and concluded each post with suggestions of what to pray for that day.
40 different devotionals will not be a quick read, of course, but I recommend starting at the first one and wending your way through these 40 meditations on Jesus' words in John.
Charlie also has a very helpful post with practical help for fasting.