Pandering

Advertising, consistency, and quality are three strategies to getting more readers, but promotion's a screwy subject since advertising can get expensive, and consistently posting high-quality pages or strips requires a lot of time and work. There's a more efficient strategy, though, which is pandering. I'd probably trash someone's webcomic if they do it, but I'm not gonna say that a creator's wrong for valuing increasing their readership over pleasing critics. Anyways, if you choose to go this route, here's a list of some of the most popular forms of pandering.

LGBT

There's a new review site called Yes Homo that only covers LGBT webcomics, and there are a ton of them out there. There are also a lot of webcomic fans who specifically look for LGBT webcomics to read, either because they're LGBT themselves or because they're into yaoi. This one's really easy to do, because a creator can just add a token LGBT character, or have one of the existing straight characters come out. You can also help advertise this to potential readers by adding the letters "BL" (boy love) or some equivalent to your webcomic's banner, and you can make it extra clear by showing two people either kissing or about to kiss.

Furries

You can get your work promoted on The Belfry, FurAffinity, and WikiFur, and all you have to do is draw your characters as animals. There's a really dedicated furry community online, and they can't seem to get enough of this stuff. Like, Furry Experience is one of the most popular webcomics on Smack Jeeves despite being a mediocre religious comic, and all of its fans are furries who probably only checked it out because it has the word "Furry" in its title. And if you don't know how to draw animals, you can just add ears and tails and turn your characters into catboys and catgirls.

Fan-service

This one's harder since you do actually have to be skilled at drawing anatomy. Although, on the other hand, it makes the writing easier since you can just focus on showing T&A. You want to have a variety of body types and personalities so that everyone's tastes are catered to. If your art's good enough, you'll be creating fictional boyfriends/girlfriends for your readers to fantasize about, and that puts you in a great position since you're the one responsible for their "relationships." You can also make your webcomic X-rated if you want, although it's probably more lucrative to charge money for commissions instead. Another tip is that you can get ranked on Top Web Comics by using sexy drawings as voting incentives.

Fetishes

The idea's to cater to a really specific audience so that you don't have to compete with other webcomics for attention as much. This strategy probably yields a smaller readership than the others, but the fans you get are really dedicated and likely to support the webcomic. One example of this that comes to mind is the inflation webcomic Craving Control, which got fairly popular even though it's just drawings of a chick eating a lot and getting fat. (The Webcomic Relief has a video review of it here.) And you can always just post pages under an alias if you're concerned about getting labeled as "the weirdo who draws a fetish webcomic."

You can also combine multiple strategies, or even do all of them if you want your webcomic to be as popular as TwoKinds. And if you use paid advertising to broadcast your strategy, like putting a half-naked chick on a banner for a fan-service webcomic, then you'll be giving your webcomic a huge advantage over more conventional ones. Still, when pandering, it helps to be familiar with the fundamental aspects of making comics, as while you can mostly get away with half-assing it, your readers will still expect some level of competence.