I find that qualitative research provides the best information in most cases. Usually this is done with unstructured, in-depth interviews or focus groups, and is best carried out by an independent researcher who has interviewing skills and the ability to remain completely objective. Other research includes customer satisfaction measurement, surveys by mail, email, or in store.
However, there is a lot you can do yourself before paying for professional help.
If you need more information about your customers, please read this article about how you can do your own research. Please ring me to explore these ideas further. I am happy to help.