To give you a sense of how long it took me to get it flat (although it's different for everyone and depends on how often you work on it – mine didn't start improving until I started doing it all the time), check out my pics (with dates) in this post: http://thepoleplace.wordpress.com/2011/12/31/december-update/
To prep, make sure your back is warm and well stretched. Practice bridges on the floor and work on shifting your weight over your shoulders to give them more of a stretch and help strengthen them. Another stretch I like: stand with your back to the pole (I put more of my weight on one leg and leave the other one slightly bent). Grab the pole just above your head, and arch your back, looking up at your hands. With your back still arched, slowly (carefully) slide your hands up the pole so that your arms are extended. You should feel this in your back and your shoulders, and you might not be able to fully straighten your arms depending on your flexibility so don't push it. If you're doing it with one leg bent, switch legs and which hand is on the bottom on the pole. It should look something like this: https://www.studioveena.com/photos/view_photo/4f054d91-ee78-4ac9-82ec-127c0ac37250
Now for the crescent. I don't grab the pole behind my back – I grab it behind my head. As I reach back, I also tuck my head forward to get a better grip and get my hands a little higher so my head isn't in the way. Then I push and arch. Hope this helps! Let me know if anything was confusing. 🙂