Planning a wedding includes a lot of moving parts and for most people, hiring a lot of different vendors. It can be confusing to know who to hire when. What follows below is a rough timeline, it assumes a one year engagement. If you have less time, don't panic. You may be a little busier the first few months of your engagement than some people, but it will all even out in the end.
Keep in mind as well that this schedule assumes that all of your vendors are equally important to you. If you really, really want a specific band, or if music is the most important thing to you, than by all means, hire the band first. You don't want to commit money to vendors you're less concerned about only to find out that you don't have enough left for the one you're most interested in.
Wedding Planner - If you're going to hire a wedding planner, do it first. The earlier you hire a planner the more time and money he or she can save you with your other vendors.
You'll also want to book your venue before hiring any other vendors (besides the planner).
For the most part, these people can all only do one wedding a day, so they book up faster. Popular bands, DJs, Photographers, and Caterers can all book over a year in advance.
Unlike your 10 month people, officiants and florists can usually do more than one event a day, so you don't have to book them quite as far in advanced.
Cake baker - Bakeries can do many cakes a day
Transportation - If you're getting married in the spring (prom season) or want something special for your transportation you may want to move this to the 8 month category.
Day of Coordinator - If you are not hiring a wedding planner but think you could use a little help the day of your wedding or the months leading up to it consider the six-month mark as a time to bring on a coordinator.