Mrh7448 said:
Okay...first you don't have to get rid of the line work, but having it all the same thickness puts it on the same plane. Try varying the line weight between thick and thin. The thick lines will help bring things forward while the thinner lines will make it recede.
Also you have coloured Venom in pretty much all black with a few highlights. You need to look into colour theories using warm and cool colours. Adding cool blues into the shadows and having against a warm highlight it will help bring the highlight forward well pushing the shadow back. The highlights are basically the same hue and tone with black in between which is flattening venoms form.
Word. Total word.
Yes, your most recent version looks better, but I think you could follow Mrh7448's example and use some cool tones in it too, for some contrast. Shadows are usually cool, while highlights are usually warm.
Highlights and shadows also aren't about putting in an arbitrary light or dark line and calling it done. Every tone and value of a drawing represents a certain plane in a shape, and something will only look 3-D if the edges of these planes meet up correctly. The human body is made up of very complicated shapes that produce equally complicated planes, and it greatly helps if you know anatomy. I'll try to help with part of your drawing:
I've only used two tones (and a lot of smudging
t: ) , but I've got my arm anatomy guide in front of me, and thus I know how those planes should look, and thus what should be lighter and darker. (Don't quote me on the lower arm though. The lower arm looks funky. I hate lower arms...)
Just a tip - if something doesn't look 3-D, it probably isn't your rendering technique. It's most likely an issue with general planes and lack of anatomy knowledge.
Oh, and as a general tip, if something is round (like a deltoid), try to accentuate the roundness when smudging the color. Here's something quick and dirty for a comparison:
Which looks rounder?