applying graphics on packaging

What is the best approach and process for applying graphics on a packaging CAD model and then rendering it?

That all depends on what CAD package you are using. We use 3DS Max which is no different than other rendering software and graphics can be applied through Maps, Materials, etc… Others use Artios CAD and it gives you the ability to work with graphics in you CAD files as well. Depending on the reason for showing the graphics I will determine the method used. If I am just doing a concept, I will apply them in PS to a sketch. If it is production art I will either mock it up or put it in a 3D file.