if you're sketching digitally, proportions can be easily maintained by just duplicating a section of scale over and over. And you can then use transform or liquefy to shape it for depth, pretty easy once you get the hang of it. But if your real issue is simply knowing how to approach shading in a way that accents and adds depth, my best advice there is find some photo reference of a personal in a similar pose to what your trying to draw, or a creature with similar scales, or as close as you can find, and use it to get an idea of how the light wraps and creates shapes that add depth and believability.That said, I didn't really do any of that for this image, but it's the best advice to handle the issues you have mentioned.My approach for this piece was first and foremost that it needed to have a less realistic style to match the "Pathfinder" brand. So I actually just drew it in pencil rather than digitally sketching, as I've found pencil and paper are the best tools for maintaining a nice organic flow to an image and its shapes.So I worried more about the design of the creature and armor instead of believability, and added lighting that would create an overall glow and shine like a matte metal would do, but without much reflecting of light or hard shadows. I basically made it look unrealistic but with realistic principals to create an artificial kind of depth.I also knew that the image would be used over a white or nearly white background in a book interior, which is why I gave it slightly diffuse lighting, so it wouldn't look too stark on the page background, and slightly lightened the shading as it moved to its tale and hindquarters to make it look like it was fading into the lighter colored background a little, creating a little depth.I wanted the dragon to look powerful and majestic and used motion S curves and intricate design to make the whole creature seem ornate and expensive looking. If that makes any sense. Sometimes when you go all stylized it isn't about perfect realism anymore, and it becomes about using certain principles to support good old character design and line work.So yeah, basically, my advice is practice