I also do as Mike is describing.... Take off some wood from the forearm and start that final shape, inlet the rear pipe, then finish shaping the forearm. I'll also go about 2" or so up the fore end, past the rear pipe, when the rear pipe is inlet. That starts the process up the fore end. After that it's a spoke shave, cabinet makers rasp, and scraper to finish the profile. I also work both sides as I make my way up towards the muzzle end. I've found it's helpful to draw a line along the length of the stock, about a 1/4" or so down from the top which helps establish the curve uniformally along the length of the fore end, if that makes sense... I also typically use a longer sanding block to help smooth things out a bit, although like Mike said, a lot of originals are "wavy".
Ed