There's a thread on the comicgenesis forum about do's and don'ts of webcomicking so I added mine. The third "do" is actually one of my pet peeves as a webcomic reader.
Do care very, very much about your script. Script well in advance and keep re-reading it and tweaking it all the time. This is particularly useful if you have more than one storyline progressing at once. Be your worst critic and if you think that an episode is not going to work, can it.
Do realise what are the pages that a new reader is going to check:
1. The latest episode, maybe the one before last. You can't always have the best work on your homepage, but someone said that your comic's as good as your latest update, and that's very true.
2. The first 5-10 episodes. Here is where you keep or lose your new readers. Many times I've seen some author lament their low readership, checked their story, and it didn't suck. It just lacked that humph in the beginning that made you want to keep reading. Do you think that your initial episodes are crap and don't do justice to your improvement as a webcomic artist? Think of the best possible prologue to your story, think what makes you sit on the edge of your seat when you watch the beginning of a great movie, and draw 5-10 amazing pages of prologue that will be the first thing the new guy sees after the latest page. If you outdo yourself, chances are he'll put up with your so-so early work after that.
Do understand that new readers don't give a flying fuck about your characters. In your eyes Nebula Coltrane, Galactic Detective, may be the epitome of cool, so cool in fact that she can carry a whole episode just by standing coolly in a corner lighting a cigarette and making smart remarks, because she's so, you know, cool. That works for YOU. Possibly for existing readers. A new reader is just going to think, what's this shit? When is something going to happen? Why am I reading this?