Knowing what values to paint on and in your scene can be frustrating. Here's a cheat sheet. Although it's mechanical in nature, at least you will for the most part be guaranteed a result. All you need to know, is what the local color/ value of your object is (think, if all lights are off what is the value/ color of my object?) and the value of the light source. The attached image assumes a white light and these objects sit on a white surface in a studio setting. These concepts apply to matte objects. Reflective objects will be a combination of this value system and reflections of it's environment. Another rule of thumb, white objects will tend to have a fuller value range when it's lit than dark objects. Something that is close to black in local color is pretty much graphic and very little lighting if at all is needed to render it.