There is soooo much going on with Twitter its hard to keep up with it all. I'm certainly no expert (still figuring it out myself.) But here are a few suggestions:
1.) Set up a different twitter account for each of your websites or blogs. Especially if they are on very different topics. That way what you tweet will be relevant for each site and that will help drive traffic better because people will find you on twitter by the topics you tweet about. (If you had several different sites around a general topic, say HSPs; one for HSP self-help, one for HSP job finding, one for HSP writers, etc. you'd probably be OK just using one twitter account because it would all ultimately be HSP related.)
2.) Add your twitter account to the wefollow service at http://wefollow.com
They'll ask you for your twitter id and to select three categories that represent what you tweet about. It will help you to be found easier when someone searches for those categories on twitter.
3.) Download a desktop twitter app like TweetDeck at http://tweetdeck.com/beta/
This is a free app that lets you track multiple twitter accounts, your facebook account, and tweet directly from the app without needing be in your web browser on twitter. Very handy. And did I mention free?
4.) Do a little reading online, or get a book about twitter (there are more out there than you'd think.) You need to have a good understanding of twitter basics like what to tweet, when to retweet (RT) and how (did you know there was a proper way to RT, to shorten original tweets in a RT, and proper etiquette regarding when to omit someone from a RT, there's even something called "via." Basically if you want to retweet something with a long list of RTers already on it, you only include the last person and the original person and cut everyone else out of the middle: you RT @lastperson via @firstperson...
5.) The best thing to remember is tweet consistently (better to do one in the morning, one in the afternoon, one at night than three or four all at once), tweet on topics relative to your site - that helps people find you when they search for a topic, don't try to just "sell" your site or service - tweet a link to a relevant story on your blog (then let your blog sell itself.)
Hope that helps a little bit. Most importantly, have fun with it.
Peace. Live happy!