Wing LE? What MinnFlyer said.

Aileron, elevator & rudder - I scribe a line parallel to the LE on both to and bottom. The line identifies where I want the shape to end - maybe 1/4, 3/8 or 1/2 inch depending on thickness of surface. I use a 22" Great Planes sanding block with 80 grit paper. If I'm after a rounded LE then I bevel the top and bottom of the LE - about half way to the center of the LE and half way to the lines. I then use the sanding bar to gradually round over the sections until it meets profile that I want. If I'm after a pointed LE then I bevel the top and bottom all the way to the center of the LE and the "end lines".

hth - good luck.