It's not too hard (assuming that the bezel marks are engraved). Use Tesors or Humbrol modeling enamel and some really good quality fine artist's brushes. Here's my Longines Weems bezel, before and after.
Paint the marks and numbers, doesn't matter if you go over the edge of the engraving. Wait until the paint gets tacky. Wet, but do not soak, a cloth in thinners or acetone. A nap-free cloth is best, e.g. an old cotton shirt. Wipe the bezel quickly one time in a circular motion around it (to cross the markers, not run along them). Don't press too hard i.e. you must let the solvent remove the excess enamel rather than scraping it off with the cloth. Don't go back and try to remove the inevitable smear or two. Wait for the paint to dry, preferably overnight. Then remove the smears, again with a one-shot quick motion. If you have go over a smear again, wait for for the solvent/enamel to dry completely before wiping again.
Hands are best removed, wiped with solvent and then mounted (upside down for hours & minutes hands with missing lume) onto cocktail sticks pushed into a lump of Rodico. You have to work fast, not allowing the enamel to dry. You might want to thin it just a little. The enamel must flow from the brush onto the hand. Put some enamel in a cap. Don your jeweler's loupe, pick the finest brush you've got and load it with enamel. From the base of the hand outward, run the brush along in ONE stroke. Do NOT go back and re-touch it. If it doesn't look right, remove the paint immediately and do it again.
A little practice before helps a lot!