-Be consistent. Webseries have a pretty bad stigma to them in the fact that most wind up dead projects... your challenge is to prove to the average viewer that your project is different and worth sticking with. Nearly all of the "webseries" community sites that aggregate webseries consist almost entirely of dead, incomplete shows.
-Update frequently. Once a week or once every other week minimum. People can't see what you are doing, and creators tend to forget this. If you don't post anything, you will lose any viewers that you've worked so hard to gain.
-If your main production takes a while to put together, consider side projects that are related to your content but don't take as long to make. Your main production can be the "attention getter", and your side-projects can be your "attention retainer".
-Ask for suggestions! You may not get a response at first... but you will eventually gather a "cult" following. Even if it is only a couple of folks, those few individuals who care most about your project are a goldmine of information and advice. As a developer, it is often hard to put yourself in the viewer's shoes so these people can... in a way... be your eyes.
-Keep your content short. Six 5-minute episodes is far more impressive looking than a single 30 minute episode... even though the exact same amount of work is involved between the two.
-Everything you release should improve upon the previous. Your quality standards may start low, but people will notice when your content gets better with every release.
-Forums will only get you so far... and you need to genuinely contribute to the community you decide to enter. Example: I partake in the Lightwave forums (the software I use for 3d) because I'm a 3d enthusiast. When I bring up my project, I make sure that it is strongly relevant to the discussion; people will take you way more seriously that way and you may get some valuable feedback in return!
This is just from my own experiences.