So I am by no means an expert on this. This is the way the real world is. You can tell that a pillow has tufts or creases because of lights and darks. You can see somebody's high cheekbones due to lights and darks. Well, start to look at your stamping this way.
Creases are darker.
You know there's a pocket because you can see dark edges around its outline, so anything resting on anything else has a darker outline surrounding it. The stamp itself, if it's a good one, will give you clues. There will be crosshatching, dots, or a bunch of small lines where the artist who drew the image feels shading should go. On something round, light will come from a given direction, causing one side to be darker than another. Every object represented in a stamping should have shade variation to give it depth.