Reading all these replies and knowing I ignored this advice.. :')
My current project is both my first serious attempt at a comic and a long fantasy epic with a very detailed and time-consuming art style. I have a pretty busy life and keep active with many different interests (in addition to work and school) that suck up my free time, so this year hasn't exactly been an ideal time to start it either.
I know it's inadvisable, but I'm doing it anyways because 'The Herald's Soul' is the story I want to tell and I create it primarily for myself, keeping aware that it isn't likely to become as successful as if I'd approached it the right way. It's my hobby and recreation, and I get a ridiculous amount of satisfaction from simply working on it and completing a single page to add to what I have. I'm happy with the quality of the comic, and have my story planned out far enough that I feel I can maintain that, accepting the downside that episodes will be infrequent.
My decision to make this story at this point in my life might've been a mistake, but it's one that I'm growing and learning from, and I'm having a lot of fun with it.
I guess what anyone "should" do when approaching their first comic depends on their goals and expectations. Accept that you're going to make a lot of mistakes, know what you're getting yourself into, decide what you want from your comic, and plan accordingly. If you're going to ignore the rules like I did, be aware of the risk you're taking and note that it might not work out the way you wanted it to.