How to ask better questions for an email interview

Recently, as part of my responsibilities of editing my club's finance magazine, I've had to write questions for sending to very busy people, who'll respond at their leisure. Now, that exercise is easier said that done. In a live interview, one can use the feedback to adjust the pace/nature of questions, or even improvise on the spot. But in a long distance interview, that is just not possible. You are stuck with the questions you sent. And godforbid, if they are cliched/very general/beyond the person's specialization, then the person may even decline to answer them. Therefore, the exercise is tricky and needs thought. Some pointers which I've found useful are

1. Understand your theme:-This is quite obvious but in case you were not involved in the brain storming sessions which led to the theme/concept behind the publication, then get a clear understanding of it from someone involved, so that you do not deviate too much
2. Understand WHY you asked that person/decide what you would like from him:-Some people are invited for their knowledge, others for their brands and yet others because they are easily available. Decide which category your interviewee is in, that will inform your other decisions.
3. Google is your saviour:-One has NO excuse to remain ignorant about people in this digital era..
4. But try not to duplicate content of publicly available data:-Remember you are not a reporter/friendly analyst just interested in filling space. Remember that you want good original content from that person. So try not to be too close to earlier interviews.
5. People like answering about their passions:-Whether it be distressed debt, economic cycles, corporate governance etc, people are usually passionate about one or more work related aspects(assuming we can't ask about hobbies in a serious publication). Try to find that
6. For academics, read their latest research/course outlines:-Academics's interests can be gauged by their research publications(remember these take months/years to create!) and by what they teach(assuming they have a fair level of choice/discretion in that). So questioning in those areas would probably produce a very good answer.
7. For those in industry, read up on their company/sector: Remember the person is daily focusing on that sector/company and literally lives it. So asking related to that, would ensure instant recognition and act as warm up for next. The research would also supply context to explain many of the answers.
8. Try asking open ended questions instead of those to which you know the answer:These are the most difficult questions but the most rewarding. Prefer 'what'/'why' over 'how'.
9. Try to sequence the questions in a logical flow:-That makes it easier for the person to get a birdseyeview of the questions, and to structure the answers accordingly