Probably the most obvious tip posted on here.

Well, I'm sure this will seem pretty obvious, but I've only just discovered it. (so how stoopid am I?)
Instead of trying to sand out pencil marks off front/back/neck/whatever,use an ordinary india rubber. A lot easier, and surprisingly effective.
Well, I did say it was pretty obvious.

Yep....also use light light pressure when drawing pencil lines. Its amazing how deep a groove a pencil can make in soft woods

Speaking of pencils, go to an art supply store and get white ones for marking on dark woods.