When I plan a new customer research project I like to remind myself of the most important "rules". Here are those rules in a form of a small crib sheet.
Talk to your perfect customers first
The perfect customer has a problem, recognize a problem and is able to solve it.
Focus on customer problem
Don't talk solution. Don't sell. Don't defend your assumptions.
Ask about the past and present experience
No future. No predictions. No "would you" questions.
Choose a medium people are comfortable with
Face-to-Face is the most informative. A phone is easy. Online - the fastest.
Quantify your research results
Do research regularly. Iterate on the process. Look for patterns and commonalities.