Peter's Model Railroading | Articles | Techniques | Applying Decals
Preparation

First, make sure the paint of the model is thoroughly cured. I like to wait at least a week. Usually, if you can still smell the paint, it's not cured yet. Next, I spray Testors' Glosscote over the area of the model that will receive the decals. A single light coat is sufficient. The surface needs to be shiny to make it easy to slide the decal off of the decal paper and on to the model. I let that cure for at least 24 hours, usually longer. Try to keep the sprayed model away from sources of dust.

(external link: Testors' Glosscote)