I know when you get engaged, you are so excited, you buy tons of Bridal magazines, tear out pages of wedding gowns you like, start writing a list of your bridesmaids, and the excitment continues (smile) The best advice I always give my clients is to establish a "budget" first. I know a lot of times when I ask the question " what is your max budget" the answer is usually I dont' know. Without a budget it is hard to determine which one of your wedding dreams will come true. There is nothing more devasting then for you to get in the planning process and half way thru find out you do not have enough money and have to cancel some of your "must haves " only because you never created a budget.
This also allows your planner to know which vendors to pair you up with, instead of pairing you with a photographer that is so far out of your price range, or pairing you with a cake decorater who works with small budgets only, but yet you were able to afford the bakery that make custom over the top cakes.
Also I suggest having at least 25% of your budget accesible, before you even start the planning, so you can retain the vendors that you love without, having to cross your fingers that do not book another client on your day. Having a budget helps you save money, because you have a gage and control of what to spend on each service, without over spending in one area and not having anything left over for your other vendors.