I like to follow the grain like some have said, in the sunlight makes it easier. Once I have a center line I use a circle template and mark circles along the center line, then use a straight edge to connect the outer edges of the circles, if you mark enough you follow the center well enough. It is also a good idea to use a drawknife to work the profile, you know your following grain then. Takes time but a good snakey stave is worth the time.