If the reception location doesn't come with a catering service, then choosing a proper cater is very important. Caterers prepare the food, control the serving staff and time each course as it goes out. You don't want your wedding guests to remember your wedding by bad food! However, it is not hard to find a good caterer, but you should do so about six months prior to your wedding.
When choosing a caterer to get a good feel of their style. Some caterers may have a certain style, such as locally grown, or a specific cultural food theme. Describe the theme of your wedding and, if you know, the type of food you want and see if they feel confident with it. They should have a portfolio of pictures you can browse through to see if you like the presentation. Ask how many weddings they have done as well as the size of the weddings they have catered. You want to choose someone who has served weddings your size. Make sure they have a staff big enough to accommodate all of your wedding guests. As for presentation, you will want to see what they will be serving everything on, from plates, to forks and knives to salad bowls. Also, check to see if there is an insurance for these items. Ask how much time they will need for set-up and break down, because that will affect your cost as well. If you think you've found the right caterer, set up a time for a tasting.
The caterer should layout the charges for everything after the tasting. This should include the cost of food per person along with what exactly is in each dish and the charge for ALL staffing (caterer, waiters, bathroom staff, etc). Before signing the contract, double check that the tax and service charge, if applicable, is included. After you put down your deposit, you should sign the contract in the weeks coming. This will detail everything in depth.
First, decide if you will be serving brunch, lunch or dinner. Dinner will be the most expensive, or cocktails with hors d'oeuvres. Brunch is a lot cheaper to serve than dinner and could be a good idea for a couple on a budget. Served with mimosa or a bloody mary bar, this can be great following a morning ceremony. Omelets, breakfast meats, fruits, toast/bagels etc. can be served or set-up buffet style. It is possible to make this a very nice brunch reception. You may also choose to serve a nice lunch which is going to cost a little more than brunch, but still less than dinner. Gourmet sandwiches and salads can turn out quite nice. A cocktail reception with hors d'oeuvres is good for large weddings with evening ceremonies, as a large dinner will be quite expensive. The cocktails will keep people dancing to the DJ and enough variety of hors d'oeuvres will fulfill ones appetite.
When having a dinner reception, there are many different ways for the food to be served. The most popular and formal is sit-down service. Having the food brought out is a lot more convenient for wedding guests rather than going up to a buffet. It also prevents any spills/accidents. The food may come out on individual plates or on large platters for each guest to choose. Buffets allow guests to choose their food, but you never know how much will be eaten of each. It is good to have staff with the buffet to help the flow and serve equal portions to each person.
When planning the menu with the caterer you will want to pick food that is in season during the time of your wedding. Food also fluctuates with season, so the caterer will be able to give you a better price estimate of the dishes. Keep in mind that you are serving a variety of people, not just people with your taste. There are a few things to avoid when choosing your dishes. Stay away from exotic foods and fish. Leave out spicy food and any ethnic spices/food. These should only be included if you have other options as well. Plan your hors d'oeuvres and cake around the main course. The main meal is hardest to plan. If you choose a heavier main dish, you will want to serve a light hors d'oeuvres and vice versa. You should also have some options for vegetarians, vegans or people with gluten intolerances. You may ask on the invite if they have any food intolerances.

Many caterers also provide other service such as bartending and even your wedding cake. When booking your caterer, ask them if they also provide dessert and cake. If not, then ask if they can recommend a cake bakery and coordinate with the cake bakery to pick up the cake.
If children are attending the wedding, keep them in mind as well. Most caterers offer a few options that are appropriate for children. Even if the only children will be the flower girls and ring bearer, it is still thoughtful to provide a separate option for the children. If your cater is also providing the cake, you can ask if they have an alternative dessert option to the cake for the children that will be at your reception.
