Ask a friend if they have worked with someone they would recommend. If you can't get a recommendation, then start by interviewing brokers who have certifications in the type of real estate transaction you intend to purchase.
If you can't obtain a broker who comes to you by word of mouth, then I would suggest that you first consider working with a REALTOR who subscribes to a real estate code of ethics. From there, look for a REALTOR with a Graduate of Realtor Institute (GRI) designation. Word of mouth is your best bet, but there is nothing wrong with conducting interviews to find the broker who will work best with you.