Materials
2000 ultrafine sandpaper/wet n dry.
For flatting out to a smooth finish
Two pack lacquer
This gives the best finish of all lacquers but must be compatible with you base coats, it can go on top of cellulose paint, but always test any other medium. The ready for use lacquer isn't quite as good a finish, or as hard wearing.
Hand glaze/or T cut
Used for buffing up a nice shine, use the blue bottle Tcut as the red stuff softens the paint.You can also get rubbing paste.
wax
A good quality car wax applied to the finished surface will keep the lid looking good for years.
Spirit wipe
Use this to clean the surface of your lid during painting to remove any glue left behind when masks are removed etc. But beware, if the paint is thin say on a drop shadow it may mark it if you rub to hard.
Masking Tape/Films
Various forms are available, the low tac stuff is best but costs more. 3mm pin-striping is handy for intricate shapes, use the plastic stuff not the paper, and don't pull to much when applying as it can stretch out of shape. I often use frisk masking film for cartoons & graphics, as you can draw on it before putting it on the lid surface which is a lot easier. Although it can be tricky placing it in the correct spot. Also latex masking film can be used by brush painting it on, some can be sprayed, but I tend not to use either. I use liquid mask for small areas only. The best thing to do is see what suits you best and go from there, there are literally hundreds of different masking possibilities.
Medium
I tend to work with cellulose, most auto paint suppliers can provide half ltr quantities of primary colours to get you started, from which you can mix your own colours & hews. However there are many new products in ink/acrylic form which are probably just as good. What ever you decide ensure you stick to it and avoid any surface reactions encountered by mixing different types the one thing with celly is compatible lacquers are easily available.