There are some excellent responses here already so I'll just add this. Customer discovery interviews with your actual customers will help. Customer discovery is part of the lean start-up and business canvas development. A key takeaway in conducting those interviews is to know what your purpose is before starting the interview and then ask "why" five times to each primary question. Each answer to the "why" question will uncover more information, helping you get to the true root of the answer.

Good luck!