NOTE: Since several people have asked, no, you do not need my permission to link to this page :)
To start off, before you read the following rant, you must know that these are merely my opinions. So if you don't want to hear me whine and/or offer advice, simply don't read them :)
This list is subject to addendum at any moment's notice.
In internet years, I'm an old fogey. With that said, I tend to take my webcomics rather seriously when it comes to how they are written AND presented. No, I don't mean it has to have pretty art or that the story has to be some epic fantasy with glorious Tolkien-esque battles. I mean it has to be relatively easy to read, and follow, and (most importantly) quick to access when I visit your home page.
As you can imagine, I tend to be pretty picky with my comics (printed zines included!). And there are a number of simple things that I think could help people who want to make or are making webcomics.
And I'd like to note especially: most of these are based on what I've encountered with reading other people's comics. However, some of these are what I've encountered when I was drawing Blue Zombie. I am not immune to my own criticism.
So here's a nice list of things I personally think you can do to aid in your gaining (and keeping) readers.
Comic stuff
Determine your webcomic's "niche". This way, you'll be more likely to cater to an actual audience instead of failing to attract anyone at all.
Resist the temptation to try and "out-do" other webcomics. Trust me, there are some that apparently try to be more controversial than Penny-Arcade and Questionable Content (and, in some cases, come outright and say "How can we be more controversial than Penny-Arcade and Questionable Content?" I don't make this stuff up!)
Okay, here's a tough one: putting sexual content in a comic is okay. BUT resorting to everyone in your comic spontaneously having sex is unnecessary (this has happened in a lot of webcomics I've read. I immediately stop reading them when it gets to that point.)
Tell your friends about your ideas. They can tell you what works and, more importantly, what doesn't. It's always nice to have someone to bounce your ideas off of.
Color is your best friend and your worst enemy. Color can really add character to your comic. It can also quickly kill your comic if not used properly.
It is best to stick to a simple panel arrangement. I say this because some creators--even "professionals"--have REALLY mucked up a comic's readability by having confusing panel arrangements. There is nothing wrong with a strictly simple vertical or horizontal panel flow. I mean, for pete's sake, newspaper comics have been doing it for years.
Be open to your readers' feedback. Sometimes, what they have to say about your comic can be insightful, even if it is written in a negative tone. And sometimes, even a simple email about how they like your comic can brighten your day.
Collaborating
[ Several friends are seeking to collaborate with someone to create a webcomic. This section is for them. ]Collaborating on a webcomic can be a good idea. However, you should always be prepared to have to do something yourself should your partner(s) not pull through for some reason or you can't find someone to collaborate with.
Don't feel bad when no artist wants to draw your webcomic. There are about a million others who are having the same problem. There will always be more writers with an "epic story" to tell than there are artists... and let us not forget that some of those artists are writers as well!
If you do find someone to work with, try to schedule some actual face time. An hour in the same room with them going back and forth over ideas is worth more than three hours over instant messenger.
Be willing to listen and use your partner's ideas, but don't be afraid to put your foot down. Don't be an control freak, but don't be a pushover either.
Make sure the process is rewarding for everyone you work with. When you get positive feedback from readers make sure to share it with your cohorts. Tell them when you think they're doing an especially good job. Do things within your means to keep them motivated, even if it means giving them a break or buying them a meal. You are a team, afterall.
[ Several friends are seeking to collaborate with someone to create a webcomic. This section is for them. ]
Website stuff
Learn basic HTML. Honestly, it's not that hard to learn a few simple text, anchor, and image tags. This will save you a lot of headache when something goes wrong with your website and you have to fix it.
Learn some basic web design. Nothing too drastic, just simple ideas like having all pages use a consistent layout, how to justify your text to one side and space it properly for easy readability, and how to choose a simple color palette that won't make me go blind >_O
Have the most current page of your comic easy to find and read once people enter your website (preferably on your home page!). This is because this is most likely the page they are looking for, or the page that will draw them in and want to read your comic if they are new comers.
Which leads me to another point. Forgo that "Artsy-fartsy" menu with a million and one graphical links to fifty billion pages on your website. SIMPLE TEXT LINKS CAN BE YOUR FRIEND! (They are also easier to read and interpret)
Have the First, Previous, Next, and Last links easily accessible on every archive page in your comic. It should be easy to navigate through your archives (it sounds like common sense, but some people seemed determined to make it impossible for people to actually read through their archives)
Don't load your website with tons of graphics. It makes waiting to see the main attraction a lot longer (and, if you're paying for your hosting, increases your bandwidth bills)
Software & Material stuff
Stick to software and art supplies you know and are comfortable with. It's okay to follow on another person's suggestions, but don't fall into the "OMG if I want to be good, I'll need this software coupled with this pencil and these inks!" trap.