I am lazy and this has been done before, so I highly encourage you to read this: http://hci.stanford.edu/courses/dsummer/handouts/NeedFinding.pdf
I think it answers all your questions.
To summarize:
Find your users: the average user, the extreme user, the casual user, the expert on the subject ...
Ask questions:
- Be as open-ended as possible
- Let the people educate you:
- Ask people for comparisons instead of evaluating on an absolute scale
- Avoid personal bias, because people are not very good at self reporting
- Be concrete
Good examples:
- “I don’t really understand coffee chemistry. As a food chemist, can you explain to me how coffee ‘works’?”
- "How much did you exercice this week?"
Bad examples:
- "Is the daily update an important feature to you?"
- "Would you like something more intuitive?"
- "How often do you exercice?"