Clean with medium hot water and let dry. If you are sanding, you can finish up with 240 to 320 grit depending on the type of wood, or if it's the actual glass.
Glass looks horrible when sanded...it just turns grey. It will turn translucent again once the finish is applied...don't worry.
Spray with Helmsman Spar Urethane, in light coats.
If you are doing a raw bow, spray 3 coats of gloss, and then finish up with satin. The gloss makes a harder finish, which is more durable.
Do a search on the word "spar" or "helmsman" and you will get a ton more info...
Take Care,
Marc