I use 180 grit abrasive belt material folded around an 1 1/4" wide X 1/8" thick piece of maple (about like a paint stir stick) to round the edges over. It's slow, but gives me excellent control. Though I use files and rasps extensively for shaping the riser, I seldom use them on the limbs. The only exception to this is when I need to trap the limbs to hit weight. In this application, a file cuts flatter and faster.
At any rate, work from riser to tip like the other guys said, and take your time.