Question: what are good at question?
Answer: Relevant. A good question is relevant. ... 
Clear. A good question is framed in a clear, easily understandable language, without any vagueness. ... 
Concise. A good question is usually crisp and concise. ... 
Purposeful. ... 
Guiding But Not Leading. ... 
Stimulates Thinking. ... 
Single-Dimensional.