I would say that a search of Virtual Assistant Forums for 'Twitter' (use the search link in the main menu, or better yet, the 'search forum' option inside the Social Media Marketing topic section) would bring up some
great resources and information.
Other than that, creating an account and following those you know is a good start, just to see how others are using it. If you aren't sure who to follow, once you have a Twitter account search for 'virtual assistant' and start following the people who will show up in the search returns.
You could also search Google for '
Top Ten Twitter Tips' to get some nice, condensed info on how to make the most of it.
I hope that helps

Sometimes you just have to jump in...