You may or may not know about the vast (vast, vast) writing community out there. As a writer, you should know about it, but the question is: how much should you network? You can have too much of a good thing in this case. One can spend countless hours talking with other writers online and not get a single word of fiction done.
On the other hand, networking is great. It lets your voice be heard and you make connections you might not otherwise make. You build friendships, you practice your writing voice every time you say something out there. You can learn a lot about writing on blogs and forums. I learned a TON this way.
So, if you're interested in expanding your network, here's a link to QueryTracker's blog post on The Writing Community. They list a few of the big sites you should at least know about.
And then there's Twitter. You either love it or you hate it. My personal opinion is: if you enjoy it, do it! But if you drag your feet every day, making yourself say SOMETHING, then it's probably not for you (and your tweets will reflect that).
You should give Twitter a try, if you haven't already. (And even if you have) here's a Writer's Starter Guide to Twitter (or: everything I wish someone had told me when I first started using twitter) by Justine Musk.