I'll admit, I don't know so much about gaining new readers. I do have some tips on reader retention, though. Some of them are pretty basic, so don't be offended if I point out something that seems common sense.
The web site appearance and editing are good to think about too. A good looking site that's easy to figure out navigation on may not win you new readers, but it may help you retain those you get. Same for keeping to your update schedule. If people don't know when you're going to update, they'll either show up a lot to see if anything new has been posted yet (unlikely) or only check back on occasion, read whatever's new then if they want to, and go. That's less of an issue with you having a backlog, but consistency sticks with people.
Oh, and if anyone spots a typo, see to it promptly. It may not be an issue with you, but it looks pretty sloppy to have people point out an error and it still be there a week or month later.
Another thing that helps is if you have a couple buddies that read your work and have serials of their own, or someone with another thing just likes your stuff. If you get someone else going "Hey, here's something I read" on their serial, it can send the occasional people your way. Given that my audience was mostly premade from Legion of Nothing and Worm, having them link to me was essential. Also, those two have had a number of readers who found the other from the link.
And this is more of a thing for when you have fans, but I find that having a little bit of a sense of community, usually through the comments, can be helpful as far as bringing readers back every day to check on new developments, and it helps the story stand out a little better in people's minds. It makes a story even more personal, in its own way. Readers may do this on their own, but one way you can nudge them in the right direction is to have a comment of your own on a post that doesn't expand or give away anything, but nonetheless helps get people thinking about discussing their own view of it. Wildbow frequently employs this.
Oh, and having a TV Tropes entry wouldn't hurt as far as new readers. That's one I reader-gaining suggestion I thought of. Perhaps look into similar communities that might like your story and mention it in the forum there. Even game forums.
Hope some of that is helpful.