One interesting thing of note. Someone mentioned above that his painter recommended roughing up the surface a bit with a Scotchbrite pad. Provides a good "tooth" for the decals to hold on too.
But high end model makers do just the opposite. After painting on the color coats, like camouflage, and before the decals, they spray their models with a gloss coat, which allows the decals to "suck down" and adhere to the substrate better, especially at the edges. Then they apply a matte clear to knock back the high gloss. FWIW.