tips on how to improve

Also another question, which I'm looking for opinions In a manga I'm working on, which the settings is a post apocalyptic World. When it comes to drawing firearms, how much detail is needed? Like I know the gun need to look like a gun, but how real does it need to be? Or does it depend on the artwork of the manga?

Enough so that it looks like a gun, but there is no need to stress yourself over it. Just add as much detail as you would on anything else...

Question: What part of the human body do you begin to draw when you begin drawing your character? Most of the time I start at the head, and others at the body

I draw a rough sketch of the "skeleton" usually beginning where the weight is displaced most, then shape in a outline, focusing on the body, and usually the last part is the head for me. So in nutshell, body first.