Ten Best Practices for Teaching Online
10 ideas for those new to teaching online, including being present, creating a supportive community, and a number of tips on writing good discussion questions.
Developing Effective Questions for Online Discussions
Tips for online instructors (and IDs) on how to write questions for online discussions. Three types of questions are identified: factual, thought (Socratic), and problem-solving. By Judith Boettcher--this is now part of the book "The Online Teaching Survival Guide: Simple and Practical Pedagogical Tips"
How To: Write Questions that Stimulate Discussion | Thinkfinity
Although this is about questions for discussions in a community, these are good basic guidelines for online learning discussions too. These could work as guidelines for a student-led discussion on how to write good questions.