Things I've done to attract more readers and thoughts on them
1. Advertise: Lately, I've tended towards one day ads on comics with similar themes. I usually try to get my ad up on that comic's update day. That way, I catch more of their readers. This has done well by me. Sometimes advertising on smaller comics is better than bigger. One or two readers is better than three hundred casual browsers who never come back.
2. Guest comics: We did a guest comic for Flipside and it brought in a nice amount of traffic. In fact, it continues to send people our way on occasion.
3. Beg other comics for spotlights: Ursula Vernon over at Digger mentioned Mysteries of the Arcana briefly in her comic's blog. We're still getting the occasional hit from over there. Likewise, Shadowgirls and Rival Angels both did a small write up of MotA and that sent some good traffic our way.
4. Groups: Mysteries of the Arcana is a member of 910 CMX, the Webcomic Planet Collective, and TeenBit. By far, the various teenbit comics are, together, our biggest referrer. We're not getting a lot from WCPC right now because we don't have a link exchange box up but when it was up, that brought in some good traffic. 910 CMX brings in a smaller but respectable number of visitors.
5. Lists: We've joined most of the lists out there. thewebcomiclist.com, Belfry, choice, etc. We get some nice traffic from thewebcomiclist.com and Belfry, usually a few hits a day at least. Not huge but nice.
6. Twitter: This might surprise you. Because of the habit people have of friending anyone who falls into a certain category I think I've picked up a few fellow webcomickers as readers. They friend me because I do a webcomic, see a twitter I send out noting the comic is updated, and check it out.
7. Topwebcomics.com: I can say without a doubt that being on the front page of topwebcomics.com gets you a lot more hits than being on the second or third or further back page. Topwebcomics.com is one of our biggest referrers. We keep within the top 100 by having daily vote incentives. Its easier than you might think, too. For a while, I ran screen shots of my comic's characters done up in Sim3 with clever captions. Right now, I'm doing a stick figure parody comic. If you're the sort of person who keeps a buffer, why not do daily previews of your next comic? Show a frame a day.
8. Links: Similar to spotlights, links from other comics continue to bring in a nice flow of traffic. Bigger comics tend to bring in more traffic, of course, but almost every comic that links to MotA sends us a few readers each week.
9. Word of mouth: Or, more, word of blog. A lot of people out there list their favorite webcomics on their blogs' front page, or set it up so that the RSS feed from their favorite comics show up in their blog. You could ask your readers to do this, but I suspect it happens more organically.
10. Be punctual: Seriously. Show you're reliable. Show that your comic will meet deadlines and is worth investing in. That, along with a good comic, will keep the readers and draw new ones in.