1. Know what your essential question is before you start

The essential question is the one you want answered (eg, will you marry me?); everything else is a means to get the answer. A good inquiry usually has only one essential question.

2. Using questions to clarify

What the other person has said shows that you are listening, prevents misunderstanding and often help the other person realise what they are saying themselves. 

3. Start an inquiry with broad questions

As these will help you find out more and also reveal less about your assumptions. And, unless you are testing knowledge on a specific subject, they will also tell you more about the other person. 

4. If you are trying to gain rapport

Use questions that build on what the other person has said (eg, and what did you feel at that moment?).

5. How you ask the question can be more important than what you ask

There are at least ten different ways of asking 'what do you want?', each with a different meaning (how many can you think of?).

6. Tangential and hypothetical questions

Help get a conversation out of a rut and encourage creative thinking but if used too often people might think you can’t focus or are trying to be too clever.

7. If a question is not it answered, let it go for the moment

It's generally wiser to come back to it later from a different angle than turn it into a big issue.

8. A list of questions helps organise a discussion with an unfocused group

Agree what needs to be answered and let them debate each question in turn: you will be surprised how much easier it is to get clarity on where there is consensus and where the real differences lie.

9. The beautiful question begets the beautiful answer

If you don’t like what you’ve heard, think about a different question before you blame the answerer.