My first piece of advice is, know what your budget is before looking at anything, including your dress. Both WeddingWire and The Knot have easy-to-use budget planners that are free. How these budget planners work is this: you figure out how much, over-all, you can spend on your wedding and reception; put that full amount into the budget planner, enter the estimated number of guests, and let the planner do the math on how much to allocate for each item associated with your wedding.
Once you've done that, look over the estimated amounts you should spend on each thing according to your budget. If the estimated amounts look fine, great. That usually doesn't happen, though, so you'll have to play with the numbers a little bit to give more money to the items that are important to you.
Okay, your budget is set, time to move on to the actual planning stage. I would advise you to start by looking for your dress. The dress is going to set the tone of the rest of the wedding so it's best to get that chosen first. Here's why - let's say you've been dreaming of a winter wonderland wedding with all the decorations - and your dress - in pure white. You go out and buy or order everything in pure white and then go to try on dresses only to find out the pure white color you've been envisioning makes your skin look blotchy or washed out. Now what do you do? Spend the day looking like an extra from a vampire movie or spend money to change the color of the decorations? In my opinion, both options are unacceptable.
Next, go to your appointment with an open mind. Just because you've been dreaming of an ivory satin mermaid style with a lace-up back, doesn't mean you're going to look good in one, or be able to walk in that style. Be willing to try other styles and colors. Listen to your dress consultant, that's what they are there for, after all. They see different body types all day, every day, and have a pretty good idea of what style of dress will show off your body type the best. If you go in with a set idea in your head and refuse to try anything else on, you're going to end up not choosing a dress that day and possibly trying on hundreds of dresses that are the same style at other stores. Whereas if you just had an open mind going in at the first store, you'll find your perfect dress in a much shorter (and less stressful) amount of time.
My last piece of advice about the dress is to never, ever, try on a dress that is over your budgeted amount. Chances are good that it will be the dress that you fall in love with and you'll be too disappointed that you can't afford it that no other dress will compare. Or, you'll decide that you just have to have it and will find the money for it 'somewhere'. Going that route leads to arguments and tears; whether you're arguing with your fiance, your parents, or your great aunt Josephine. What's more important to you in the long run, going over your budget for a dress you'll be wearing for only one day or starting your marriage out with no hard feelings over how much your dress cost?
Trust me, go the less stressful route and, if it's over your budget, don't even try it on in the first place.