Materials and texturing make or break any rendering. Much skill and a good eye are needed to get the most out of materials. It helps to be a very good observer of the surrounding environment around us. Today, smartphone cameras are good enough to capture photographic textures and image maps whereever you are. Not to mention that you can also capture decent quality video, which can also be used in a pinch.
Materials and texturing is really a layered process. Typically a “clean layer” or series of layers are created, and then stress or weathering-related layers are created separately. Further, special driving layers, such as a grayscale displacement or specular map, are added into the file.
When creating a texture or material intended to match a real world experience, its always best to start with a photo; using a photo is faster and much more accurate than attempting to paint the same thing. Further, you can combine techniques as needed, using the best of both.
Materials use shaders and special algorithms to accomplish their effect; it helps to understand what those algorithms are, how they influence the final result (both in terms of speed and image quality), and how they best suit your needs. Some shaders can be very complex, and thus, very slow. That said, there may not be an alternative method to achieve the effect of a particular shader. Its up to you wo know what to use, and when.