Following are online resources on how to's and tips/tricks:

Tips on Role-Playing & Technology Use 
The Five Cs of Role-Playing presented by George Mason University.

Role Playing/Simulation 
Classroom techniques, practices and behaviors presented by the Internet TESL Journal.

Guidelines for Running Role Plays 
Geography Discipline Network presents guidelines for running role plays .

How to Teach Using Role-Playing 
Carleton College explores the issue that role-playing exercises can be hard work for the instructor, both in preparation and in execution, but the work tends to pay off in terms of student motivation and accomplishment.