There are several types of chats to know about. Live chats where everyone posts at once are insanely busy and IMHO only worth doing if they're moderated. Forum chats are laid back and slower so you have time to respond. Group chats (my personal fave) are what you make them. You can have a lightning fast pace if you co-op with other authors, or slow it down by doing one alone.
The best way to learn how to chat in a particular venue is to attend a few in that location. A chat on my group, Romance Lives Forever, can be as different as night and day depending on who's the guest. With Selena Illyria, who is a frequent guest chatter, it's insanely busy, full of laughs, hot excerpts, great videos to ogle, and recipes to make. She brings guest authors and the two-hour period races past. She's prepared ahead, and that's part of what makes her chats fun. I've had more serious authors whose chats went just as fast who had completely different agendas.
The biggest difference is preparation. Authors, know your time allotment, and plan what you'll do to fill that period. Consider how many excerpts you have, and how long it will take to read them once you post. One excerpt every 15 minutes is NOT fast enough. If you have one book, and only two excerpts you can use, you need to decide what to do with the rest of that 2 hours. Always plan for more. It's better to have things left over than not to have enough.
Readers, attending a chat is fun for us, but work for an author, even if she/he is having a great time. When you drop in and post a message it makes our day. Even if it's "Hey, jumping in for a minute while I fix dinner." There's a *live* person out there! In cyberland, it's hard to tell. If you want to hear more about a certain book, by all means say so. Don't be afraid to ask questions. I know 3D is becoming common, but so far, no one's been able to figure out how to reach through the screen and grab you. It's safe. Well, except in horror movies. ^_^
The origins of chatting were readers and authors interacting and answering questions. Now, readers tend to lurk more than interact on groups, depending on the group and many other facets. It's more of a one-sided show in some cases. If you have two hours to post, and get six comments, is that a successful chat? There is more than one way to know. If you offer a free read to anyone who emails and asks for it, you may get those same six comments (or two), but end up with 20 emails asking for the free read. The point is, have a reason for readers to follow up - by offering a download of a free read, a drawing at a certain time, the chance to sign up for your "release" list (a single email when your next book releases), a link to a special video only for those who ask. Give them a reason to check out your website, follow you on Twitter, Facebook, etc. Whatever you dream up.
If you're new to chatting as an author, here are three ways to learn how to use them.
#1 - attend a few chats as a lurker/reader, and just enjoy them.
#2 - reply to some messages and see how you like it.
#3 - sign up for a chat with a site you feel comfortable with, or where you've attended chats you enjoyed.
If you're new as a reader, try the first two yourself. You might find out how much fun you've been missing!
Like swimming or riding a bike - you learn by doing. You can watch a few people who do it well and see what it is you're supposed to do. Will you be an Olympic swimmer first time in the water? Maybe not. But get wet and enjoy the water anyway. Stay in the shallows till you gain confidence, and when you're ready, launch out. The English Channel on your first swim...? Uh... no. But you can probably make it across the shallow end of the pool. =^_^=