I'm a psychologist, and part of my job is trying to find out things from people, or what we call "research". Mostly this involves standardized experiments, but sometimes, when we want to start something new that we have no experience with, or when we find that our approach didn't work and we need to get a better idea about what the problem actually is, we just talk to people.
The first step is always a lot of brainstoming and navel-gazing, and if we are lucky this give us some ideas for what we might ask people, but sometimes we just find "samples" of people who do or have what we want to study and talk to them like you would talk to your wife about her day.
For example, if we want to study the eating behavior of overweight people, we get a few overwheight people and just ask them what they consciously know of their own eating behavior.
During these conversations, we will notice certain things (what all overwheight people from our small sample do) or have ideas (what we forgot to ask), and slowly we come up with a list of questions that we think might narrow the problem down.
So we find another small sample and ask them our questions, besides talking to them freely and listening to anything they might want to tell us on top of our questions. This is called a "semi-structured interview". It has some questions that we want addressed, but it is also open for things that come up that we didn't anticipate.
Then we either refine our interview questions or begin to create the first draft of your "instrument", which might be a questionnaire or an experiment or whatever. This goes beyond what you want to do and is rather complicated, but the above first steps are something you might try:
- talk to a small (two or three) sample of the people you are interested in
- notice recurring topics and ideas you have
- create a list of interview questions from that (so you don't forget them and ask everyone a core of the same questions, so that you can compare the answers and make sure that what one person says actually has to do with the thing you study and is not an individual occurance unrelated to your research)
- interview (and talk to) other people
- refine your semi-structured interview thingy
- talk to more people
- write your book