you've all heard that the best way to get good at something is to do it. and do it again. but it's not simply a question of hours and labor. if you want to draw comics, then don't draw spider-man headshots over and over.
draw ACTUAL COMIC PAGES: don't just draw a glory shot of wolverine punching aquaman (you know you were thinking it), because about 2% of comics pages involve stuff like that. pick up an existing comic script, or movie script or even a play/book and draw all the stupid stuff they have to draw: people shopping for groceries, a science lab, kids riding on a bus, kids riding on a bus that is smashed by a giant cyborg lizard (ok, sometimes you do get to draw the fun stuff, i mean it IS comics).
kissing: if you can draw 2 people kissing in your style, and make it both physically and emotionally believable, then congratulations! you are a goddam genius. everyone else, GET ON THAT.
different body types: sometimes women are young and hot and dress like ninja hookers. sometimes they look like actual women. it you can't manage to do both, YOU'RE DOING IT WRONG. if you draw a team of superheroes and their silhouettes are indistinguishable, YOU'RE DOING IT WRONG. (unless you're bruce timm. you can do whatever the hell you want, because bruce timm.)
cars and stuff: do you plan to draw every story in a cosmic void? are you independently wealthy? i hope so, because no one else is going to pay for that crap. figure out how to draw cars and trees and buildings. if you live in a desert where there are no cars or trees or buildings, look into something called the internet. if you can't get everything you need from real life or the internet, then you have bigger problems than drawing comics.
structure: did you draw a really cool shot of luke cage? can you do 20 more panels of luke from different angles? smiling? shouting? pooping? hey, i don't know, people always talk about "realism" and realistically, everyone poops. there's a book and everything. but i'll give you a pass on that one. all the non-pooping stuff? DRAW IT.
reference: pick up a goddam history book. yeah, you. you may or may not have to draw a samurai riding a sabre-tooth tiger's back one day. i mean seriously, isn't that EXACTLY why we all got into this? so why not be ready for it?
anyway, i'm too tired to go on, but that's enough to start with.nobody's perfect (except rodolphe guenoden), but if you're not working on these things, just stop drawing right now. because there are a lot of other people out there who are!