>>7622270 (OP)Heavier lines in shadow areas
Lighter lines in light areas
Variation of lines
Nice curves and confidence of line
Style
Etc.
you just gotta ink. The more you ink, the more it becomes second nature to do this stuff. As someone who just recently found their voice with art and inking, just trust me on it.
Some people will take longer than others, even with the same amount of practice. Itโs just how it is. But just keep going. Have comfort in the fact that you WILL get there eventually. Everyone can draw, its not something your born with, it is a skill to develop