Increasing your readership is a little like trying to find love. You can't force it to happen; the best you can hope for is to improve your odds a bit. And if anyone tells you otherwise, they're probably trying to sell you something.
Part of the problem is that the whole webcomics scene is constantly changing and what worked for people a year or two ago is now outdated. The message-board culture of the mid-Aughts has been replaced with social networking. Collectives seem to have fallen out of favor. Established webcartoonists rarely link to new works nowadays; not out of malice, but because they've got more on their plate now, and don't really have the time to act as talent scouts.
So, the whole popularity thing is kind of a crapshoot these days. I guess it's always been, really, but the odds have gotten longer. Some people compensate by constantly self-promoting, working the social media sites. Which is fine, but I wonder how well the introverts fare in this environment; I have trouble imagining the next Watterson or Schultz hustling for upvotes. Personally, I prefer buying ad space on webcomic sites; you get some new readers, your favorite cartoonists get a little money, everybody wins. And you get to keep your self-respect (unless your ad is just a drawing of a buxom lady's torso, in which case, self-respect probably isn't high on your priority list, anyhow).
I say all this not to dishearten, but to temper your optimism. Quality doesn't always rise to the top (ask van Gogh), and not everyone at the top is quality. But, if you constantly strive to make good comics, you'll find the work rewarding and you'll improve your chances of getting noticed; plus, the better your comics are, the more likely your readers are to share them with friends, which is still the best form of promotion out there. And remember, when you hear other cartoonists describe their paths to success, listen closely, but bear in mind that they're only telling you what worked for them.