A - Have a basic idea of what you would like... cocktails and champagne, a buffet, or a sit-down meal. With this in mind, begin your search! Keep in mind that some venues deal with only certain caterers, so check that out first. Check availability.
B - Form a first impression through recommendations of others, viewing the web, or a phone interview. You may also wish to check with the Better Business Bureau before proceeding.
C - Check out about 3 caterers to find the one that best suits you. Arrange a consultation and perhaps a tasting or a viewing of photos to get an idea of what it will look like. Get all the details of what is included (set-up, clean-up, tablecloths, silverware, napkins, centerpieces or decorations, number of servers....?) and if this caterer is suitable for your venue. Is this caterer also going to provide the wedding cake? Find out when the final head count would be due.
D - Check the references. Ask about things such as punctuality, politeness, and dress code as well as how well they liked the final product. Ask what they liked, if there were any problems, and if they would recommend this caterer.
E - Sign the contract. Make sure it includes the location, the arrival time, hours of service, plus what is included in terms of head count, food, accessories, and services. Any legal considerations such the cancellation policy and insurance coverage should also be in writing. Make sure the details of the deposit are clear, as well as how much is owing, and when it's due.