Dustin talks to about how to select various elements within the UV editor and how to find them in your viewport model. This will help you understand how the UV editor interacts with the overall model and what type of preparations you need to make in order for textures to be overlaid later.
The way you overlay your materials onto any model/object is critical to realism. The UV checker will allow you to look at the skin of an object more closely and allow you to align things properly.
In this section Dustin explains how UVs might need to be resized, relaxed, and/or stretched in order to make the texture that will be applied to flow properly and minimize artifacting.
Understanding UV islands, how they are packed in the UV editor and how packing will impact materials once applied to the model.