I found this awhile ago at Marketing Co Lab

Let’s face it, Twitter has become the best of reality television- where we all want to know the details and participate in the lives of ordinary people and businesses.  It has also become one of the best forums for sharing up-to-date information on topics of interest.  However, there are always the people who abuse a good tool.

It focus on “stupid people on Twitter” but provides a list of “don’ts” that are a good introduction to Twitter.  Often people share too much or too little.  While this is ok some of the time, it’s not something that you want to do ALL of the time.