Start by taking a photograph of a cap that has a nice angle. Usually, the resulting illustration is only as interesting as the original photo. Do consider lighting when you take the photo. Good lighting will ensure that you know where to draw shadows and highlights when doing the illustration.
You'll be able to focus on workmanship and not trying to visualize where shadows and highlights should go. Although, you can compensate for bad lighting if the conditions of the photo don't allow for nice lighting. This photo is not the best, but I will improvise and exaggerate the shadows and highlights that are visible.
Put the cap photo on it's own layer and lock that layer. Throughout this tutorial I will be using multiple layers to make it easy to lock items when not in use. I will not be pointing out when I use a subsequent new layer.
Use the Pen Tool (P) to trace each section of the hat. Do not trace the entire outline of the hat all at once. Tracing sections will afford you the opportunity to control how the gradient mesh works within each area more precisely. Use a bright color and set the strokes thickness to about .5 to make it easy to see what you are doing.
