Nothing's wrong with promoting your webcomic, although between creators it can be a touchy subject since we all want a piece of the spot-light :P.
Other than just having a great story and great works, there are various rough-work ways of getting subscribers if you really want them. And I'd say, in that case, you'd have to network all day, every day. Getting to know your readers first has a better chance of them getting to know you, and thus your comic. Don't shove the comic in their face as soon as you meet them though, you want it to be their idea to check your work out. Get to know them first, talk about other things, and if the topic of your comic arrises feel free to elaborate to your hearts content. If a real subscriber is interested, they will search or ask your background to see if you run a series, and if they like it, they'll subscribe.
Thus, with this forumla in mind, the more people you interact with, they higher sub-count possibility rises. In some cases people will subscribe to you because you've become their friend and your comic becomes an outlet for them to communicate between the two of you on a topic you both enjoy.
Course, this is the only brute-force way I know of, other than getting the luck of the draw with a popular boom like some creators encounter not far into their webcomicking career (Dang, how lucky :P)