DON'T assume your favorite restaurant knows how to cater large amounts of food. They may be stoked about the opportunity if you ask them, but without proper experience or equipment, you may be asking for a disaster.
DON'T go with a caterer who is not clear on their payment terms, deadlines, or does not have a clear and consice contract.
DON'T keep calling a caterer that won't call or e-mail you back. There are lots of other vendors that are eager to help you.
DO ask for references and to look at photos of real events they have catered.
DO expect your caterer to have a pofessional demeanor - even if they are a friend or family member.
on that note - DON'T hire a friend or family member
DO Read your contract and go over it with someone else before you sign it.
DON'T Hire somone who is a good cook and wants to break into the catering business. They likely don't have a license and insurance.
DON'T hire a caterer who doesn't share your vision. The food speaks volumes to a couple’s personality, preferences, culture and visions of your wedding. Your caterer needs to understand these things and be prepared to work within your vision, not their own. A good caterer will be more concerned with making you happy than making the extra sale. So get rid of those trying to push certain packages on you just because they fall into a higher price point.
DON'T Expect extra without having to pay for it. your caterer will go the extra mile to create what you want, but it costs them money to do so. Don't expect discounts or freebies. If you are on a budget, DO ask about ways you can make your catering service more affordable.