I usually offer a few parameters as well:
- Avoid yes/no questions.
- Be specific in terms of ideas and passages (i.e., specify page numbers).
- Ask about the areas or ideas you struggled with and/or those that really aroused your curiosity.
The latter point is key. The best questions usually arise from a sincere questioner.
Thanks to Steve Snyder for this Faculty Focus article on how to develop students’ questioning skills. This applies to both traditional classroom instruction and to discussion forum participation in online classes.