I have not studied this aside from very basic things, so here are some thoughts. First world countries are sorely lacking. Come on. Not nearly enough face/body paint in the world. But you can be certain that before we had a centralized government, way back to proto-us, there is a stage with body paint.
Body paint is a symbol. Usually both shape, color, placement, thickness, time of year all mean something for the wearer and the culture. The activity preceding or taking place afterward are generally what the paint is for, but there are some cultures that are currently utilizing tribal political organizations that wear it every day. It may communicate status, wealth (often intrinsically tied to status), or even tell of achievements. The shapes and colors are culturally specific. A line from one eye to the ear of the same side may mean something different to one peoples than to another. They can be used to identify castes such as warriors or priests or political leaders, or even farmers or slaves. It may also be used to denote emotion--maybe there are special symbols for someone who just had a baby. Body paint is mostly applied before a ritual of some kind, whether that's before a puberty ceremony or before a hunt, it could by anything. Just like with planning color meanings, body paint will be determined in the same way for the same reasons. Use your environment to determine paint colors, and use your culture's societal norms for when, where, and how they place it. Remember that outsiders looking in are not likely to know the meanings of the paint. Also keep in mind those things your society values. If the harvest is a big deal, there may be a ceremony or application of body paint. If harvesting is not considered important because it happens all the time, hunting parties may be applied with paint since the acquisition of meat is more rare. Come up with reasons why and keep those in mind as you're writing, and body paint can become an interesting, new way to portray characteristics of your culture.