I found some higher-level help for Peer Evaluations (which I would see as the higher-level goal of the Workshop activity):
- This comes from Best Practices for BlackBoard: http://www.unh.edu/it/old/media/blackboard/bb91-docs/BestPracticesforUsingSelfandPeerAssessments.pdf
- Peer assessments in on-line learning: http://www.brown.edu/about/administration/sheridan-center/teaching-learning/course-design/learning-technology/peer-assessment-online
- Peer evaluations for English (essays): http://www.nclrc.org/essentials/assessing/peereval.htm
- In my field (software engineering) there are often so-called artifact check-lists used for evaluation. The criteria are usually pretty objective, and could be used in a peer assessment. http://www.site.uottawa.ca/~tcl/seg2105/coursenotes/ClassDiagramChecklist.html
- Finally, several references mention that it's good to provide an example for peer assessment that is done before students assess each other. It's a good way to make sure the criteria used in the assessment are clear and understood by all.
The Moodle FAQ for workshops mentions some of these points (e.g., using examples), but it is mostly about the Moodle (technical) configuration of setting up the activity rather than what's needed for a good (content) of the activity.