If the stave is split (rather than sawn), it is relatively easy to follow the snakes. Put the stave with the back side up, and meticulously follow the highest point of the crown on the back. Mark the highest point over the entire length of the stave, not the center of the width, but really the top of the crown. This will be your center line. Now look for knots or cracks that you need to avoid in the final outline. Mark the center as well. Now mark the width of the easier limb first. Say 1.50" at handle fade, 1.25 at midlimb and 0.50" at the nock. That means you mark half that width either side from the center line. Also mark the width between these three points. 1.375" at 25% from handle, 0.875" wide at 75% from handle, et cetera. Once you have a few marked points for width established on the stave, connect the dots freehand. Avoid cracks/knots by swirling around them. Then do the same with the second limb. Measure width from the previous limb to transfer these sizes to the second limb, so both limb are equally wide and tapered.
The width is now established. But the tips may not be alligned with the handle. This may be corrected later, when the stave is about floor tillered. Use heat/steam to correct the string allignment.
Jorik