Everyone is looking for that magic bullet that guarantees an audience. While there is no such thing, and in fact it is likely that we will never find it, the closest we have is giving the audience a stake in the project that we're working on. That is, we need to establish some sort of way that the audience feels that it has some sort vested in the success of that project. The problem here is that we need to bear in mind that we need to allow for an audience stake in the project without at the same sacrificing artistic integrity in the same; that can be a difficult point of balance to attain, but well worth the results.
It needs to be noted that we're not talking giving control of the comic to the audience. That has been tried in the past and it predictably doesn't end as well as you would think it does. While some feedback is appreciated, especially if it's reasonably intelligent and constructive, and it is possible to give fan-favorite characters a bigger presence, it needs to be noted the audience should never be put in control of the comic. The takeaway here is that while you should listen to your fans and even implement changes they suggest but keep in mind that you are in control of the comic.
This also means that you shouldn't you shouldn't do fan service just for the sake of doing fan service; it's easy to drive readers to your comic with scantily-clad girls but that doesn't mean you should. This is your call: If you want to draw some sexy characters just for the sake of drawing some sexy characters go for it; it's your comic and you can do what you want with it. Also, it can be fun to just take a break from the regular comic and post some characters in their bathing suits. All I'm saying don't draw sexy characters just for the sake of drawing in an audience; it's a cheap tactic that while it works in the short-run can work against you in the long run.
Merchandise sounds like a weird call, but nothing puts a fan in the zone like reading his favorite comic in a sweatshirt with the comic's hero on his chest. Have some fun with the merchandise; with all of the different print-on-demand options it would be silly to not have some fun with the idea of your logo and characters on merchandise; don't limit yourself to just T-shirts. If you have a table at a convention don't forget the freebies; even if it's just pencils with your URL on it it helps to get the word out about your comic. There are a number of different options; just go a little crazy and have fun with the merchandise. And don't forget to make books available at some point; nothing makes a fan happier than a book he can smell and touch.
The key here is that you want your fans to feel like they have some stake in the comic itself. It's not enough to have a great story, likable characters, and incredible art; while that's a great start the fans also need to see that they are listened to every so often, have some merchandise, and side projects don't hurt. You don't have to change the story or artwork; just acknowledging their comments works. Doing interviews on podcasts helps, as well as having a Facebook page; anything that gives them a little slice of you can be very effective towards your success.
Basically, if you want your comic to be a success then you need to give your fans some way to feel a little ownership in your comic. Public appearances, acknowledging them, merchandise are all great ways to give your fans what they want. Remember that and you should a lot of success with your comic.