Well, everything else I was going to say has already been said so I'll say what has not been said yet. There are two things, relatively easy to do, that I would recommend EVERY credible webcomic should do if it actually wants to collect and keep a fan base:
1) UPDATE ON A REGULAR BASIS. If you say when you start the comic that it's going to be updated weekly, then by fucking god update once a week. A good majority of starting comics I see fall for the trap of the over-ambitious update schedule, realize they can't keep up with that, and then become sporadic at best taking long hiatuses between short bursts of frantic updates. THIS IS BAD. From the word go determine what pace you can actually keep up without burning yourself out or getting bored of it, and stick to it!
2) Actually acknowledge and interact with your fans on some basis. I don't mean kowtowing to their every shrill whiny demand, but they'll be a good barometer if something is being poorly received. Also people will care a lot more about your comic if you the creator actually have some sort of personality they can relate to and you're not just some nameless faceless comic-factory.
