Masking before painting?

Yup, Mckenn is right, use the clay (playdoh is fine) to cover areas you don't want to paint, then take-off the clay once you're done painting.

Exadoor- get yourself a fodder fig first, then take the modeling clay that doesn't harden ( the kind kindergarden kids use) and push a blob onto a area. Then you take an x-acto knife and gently but firmly cut away any unwanted clay. Light coats of paint are very important because the clay can lift the paint if it's too thick at the edge. BTW fodder fig is for practice before the real custom, not sure how clear I was on that. Hope that helps.