This is a resource that I use in my NMSU courses for chat activities. ~julia

Chat Guidelines and Tips

Here are some things to keep in mind for our chat:

Please be on time for the chat event you choose to attend. This means that you should log in no later than 5 minutes after the start time. The first 5-10 minutes will be social, "Hi, how are you?" time and then the facilitated discussion will begin.
Please note that if any chat event has more than six students, I may break us out into different chat rooms and I will ask for help facilitating. (Blackboard has more than one chat room in its chat section. You may need to think about class size for whole group chats. They can be interesting.)
One strategy to help in a chat with pre-assigned questions is to have some answers and quotes ready in a word processed document and ready to copy and paste into the chat.

Here are some further chat techniques from a resource titled Strategies for Using Chat:

According to research, student-initiated and instructor-facilitated chat works
better than instructor-led chat. In the chat room, the role of instructor is more like a facilitator. The instructor will challenge students to think and construct their own knowledge structure.
Ask for clarification if you do not understand something posted by someone else.
The instructor can ask: "what do you mean by saying..."
To help build discussions, instructors can say "Think about words of Student A,
do others have any comment on this?"
The instructor can keep the chat on track by saying "These are questions for
today's topic..."
The instructor can send private message to students who are a little off track by
saying "Please hold your questions a little bit, we will talk about this later."
The instructor should scaffold chat discussion. He/she can encourage students
and challenge them by saying "we are on the right track. Let's think about this

more..."
Upon entering the chat session, greet everyone and announce yourself.
Address individual people you are responding to by name so they know you are
talking to them.
Break lengthy messages into short segments, each ending with "more..." or just "..." then
others in chat will wait for you.
Be as clear and concise as possible.
Say goodbye in some manner when you are ready to log off.

?: I have a question
!: I'm making a statement
link: a link you want to share
@name: replying to someone (ie: @holly - I want to know more about your use of Google Sites)
blog:
note:
wow:
aha: This is an Ah Ha moment for me
TA: Think Aloud
whisper:
idea:

Chat sessions with 4-10 participants are quite manageable, however large groups can be very difficult to manage and are not recommended.

More than one "conversation" may develop - causing confusion and overload.
Two many users (i.e. 10+) will reduce the quality of a session.
Users with slow typing and/or screen-reading speed may find the environment frustrating.
"Shy" users can become agitated by those who "talk a lot" (similar to face-to-face sessions).
The synchronous nature of the tool (i.e. at a fixed time) means that some students may not be able to be involved. Students are less likely to be involved at first, where as many younger students are quite used to online chat environments."

Strategies for Using Chat created by Academic Distance Learning Center, Webster University, Saint Louis, Missouri. Retrieved February 14, 2011 from http://knowinsight.ccsf.edu/getAttach/89/AA-01322/using_chat.pdf