The best thing you can do if you are just starting out with a service like Twitter is to sign up and start using it. You’ll be able to figure things out very quickly. It’s so simple, in fact, that you might feel like a how-to guide is unnecessary. That’s how I felt, until I stumbled upon Mashable’s Twitter Guide Book — this is a great compilation of articles that can help you get the most out of Twitter. The articles range from the simple — “What is a #hashtag?”, to more in-depth — “How can I build my personal brand?” Even if you think you get everything there is to know about Twitter, this resource guide is worth a look.
This is a fantastic resource on Facebook — Mashable’s Facebook Guide Book. It’s a great collection of how-to and resource articles that will explain the ins and outs of Facebook. I realize basic use of Facebook is fairly intuitive (hence the hundreds of millions of users), but this online guide provides insight into things like how to run an event on Facebook and the difference between a Fan page and a Group page, information that can be very helpful if you are working to establish and grow your online presence.
Here are a few good lists of authors on Twitter:
Some of the authors I follow @52projects: