One of the best tools I've found for prep work on tiny spots is the 3M Spot Sanding Pen. This is a small (2mm or so) bundle of fiberglass bound in a handle with a screwfeed mechanism to expose more as it wears (or to adjust the stiffness of the exposed fibers). This tool is great for cleaning the metal on small chips where an X-acto knife is too tedious and sandpaper is too large. Got mine at WalMart.
Bob Hovey
Columbus, GA