A lot of good advice here. Learning how to draw well is great so you don't end up hiding your feet and hands like a certain comic artist professional. Some other things I found helpful for comicmaking:
cinematography -- I learned some basics of this in college such as keeping the camera on the same side when characters are conversing or having characters run in the same direction in a chase from panel to panel. It's simple stuff but you never really have to think about it until you're actually making something in sequence.
character design - You don't want your characters looking samey. I remember reading Scott Pilgrim and there was one scene where I couldn't tell who was speaking. I had to backtrack and step through the panels again. I know drawing the character's silhouette is supposed to help. I started looking at fashion too since my character is decked out in lolita.
graphic design - Just design in general is useful especially for laying out your comic's website, designing a business card, ensuring that your typography in your comic is readable, etc.
coding - If you choose do to the website yourself with wordpress you should know some coding, although sites like Tapastic are perfectly fine.
writing - You aren't a writer until you revise, as the saying goes. From my experience doing my webcomic, killing my darlings in a script stage is a lot easier than when you're producing the art because it takes less time to cut a panel or a whole chapter than it does to draw it. I had spec'ed my comic out to be 200 pages in storyboards. It would take me about 3 years to finish. So I decided to cut and condense the story and now things are manageable, but that was by no means an easy or one-step process. I worked on the comic for a bit. I revised. Worked some more. Revised some more.
production -- Time estimating skills and scheduling are useful. How long does it take you to pencil a page? Ink it? Paint a frame? You can use it to determine how much buffer you need and how often you can actually update.
PR - Learning how to deal with social media, ads, forums, etc.
These are a lot of the other aspects beyond just drawing your comic you can engage with to make your comic better, and I am by no means good at any of them. I'm still learning and googling as I go along.