Fundamentals can be learned from a series of DVD/s that focus around the following theme .(Im not sure of titles its been several years since Id seen them)
The DVDs were developed from old VHS tapes that are about "Drawing Comic Book Chracaters the MARVEL COMICS Way" (Or something like that.
Once you establish the fundamentals (and be careful to spend time on figure drawing because ACTION is what you need to convey and action is always tough with the figure because you have to develop a skill in rendering called FORESHORTENING (which is nothing but the recognition that you are drawing on a @D plane and items of anatomy that are coming towards you, have to be squashed down on front view so as to appear real). Its not a difficult concept but it must be learned well and early.
THEN you need some training in perspective. There are several entire volumes on that subject and all of my training was by practice and teacher instruction so youre gonna be at a bit of a disadvantage (Why not the art students league for some lessons?)
THEN, the very last thing youre gonna need is to develop a STYLE that is yours and yours alone (unless you want to copy)
The style of MARVEL comics had always been uniform, dynamic, and, to me, boring and uncreative. My personal all time favorite STYLEMEISTER was FRANK FRAZETTA. He has put together several books of comics and comic art that are still popular . I see the large bound Frazetta compilations under titles of TERROR, or CREEPY COMICS.
You should also go and try to find the old EC Comic of the 1940's. They had simplified the drawings to just the critical elements of the subject in each panel, (whereas MARVEL Comics always has every panel loaded with action and silly phrases that connote noises and such)
I toyed with doing comic journals for a lab I was working for out west years ago. It focused on geologists doing stupid things and recording them by exaggeration for our lab news letter . It led yo a brief career in San Fran doing environmental and political cartoons. It got to be demanding cause they always wanted more stuff and wanted me to delve into advert art. I had a very good job and didn't need the hassle.
You gotta recognize deadlines as controlling ALL your life
You will hate Editors for the opinionated know nothings that they are (except for a few who will guide your career-or truncate it as was in my career) .
YOU WILL HAVE FUN but it will b full of danger that is mostly swlf imposed (if you are a full-on procrastinator). YOU MUST learn to work jst like any writer . You must devote X hours a day to your ideas and execution. You will journal your ass off by keeping notebooks (or a think pad) at your side to record these ideas that just flash into your head while at dinner or walking. I had to learn that I need about 2 hours a day to develop and execute the work and I had a Thursday nd SUNDAY night deadline for each week.
SO , in summary, I consider th following the most important areas in developing your skills as a cartoonist. (Business skills NOT SO MUCH--I got fucked over several times by shifty publishers)
BUT you need to be good at
FIGURE DRAWING IN ACTION
DEVELOP A STYLE (some of these blog comics I call "refrigerator art" cause the art is so bad. Don't let that happen)
STORY-DO NOT attempt to write so much text in a panel so that the whole thing becomes like a spendi post.
STORY-keep it focused and part of your style. (I used to have a little character like a wizened old miner ) Who provided ALL the verbiage in a panel. He had a balloon with his thoughts and the cartoon was a visual of what he said. THAT WAS MY STYLE AT THE TIME.
Good Luck. Its a changing art form and the web is sucking up lotsa good (And very bad ) cartoonists. I don't like MANGA STYLE, its formulaic and cookie cutter art. I am a card carrying devotee of Frank Frazetta and EC comics (of the 40s and 50s)