This post is in response to a question I get several times a year. Due to the fact that for most couples their wedding day is the most important photography event of their lives they don't want to make the wrong decision and end up with a bad experience.
The answer to this question is multi-faceted though.
So here is some of the best advice I can give.
1. You will be spending your wedding day with the photographer. You need to make sure that they are someone who you feel you can get along with through the stresses of the day. You also need to know how they will work with you. Let them know what you want and what you expect from them. Some photographers can be over bearing, wanting to 'run the show' others stay so far in the background that you're not even sure if they're there.
2. Know their style. Quite a few studios employ more than one photographer as they shoot several weddings on some weekends. Make sure the portraits they show you are from the photographer who would be shooting your wedding. Do they shoot photojournalistic style, posed shots, romance portraits or a combination. If they only do one style I would suggest that you be very wary.
3. Ask to see an entire wedding that you photographer has shot. Normally they will only show you their really great images and then when you see your portraits you may be disappointed that not all of your images look like the 'perfect pictures'.

The next part that comes into play is the COST!!

My first suggestion is to know what you want before you even meet with the photographer. Because of the digital age that we now live in your choices are greater than at any other time.
Here are a number of things to consider that you may want.
Finished Portraits
Framing
Internet posting
Album(s)
DVD Slides show
Digital Files with copyright release
Most photographers will offer most if not all of these services for a price. Also part of their pricing is for the amount of time (coverage) that you want and the number of photographers present for your wedding date.
A big part of the cost charged by wedding photographers is because of the equipment they need to produce professional images (camera flashes can cost $1000.00, studio lights the same (per light), backdrops are $500 or more each, software such as Photoshop, not to mention the cameras that can easily run $5000 without the lenses. There is also the hours of training and schooling that most professional photographers take EVERY YEAR. The time component also is greater than you may realize. Packing the equipment, drive time to and from your wedding, and then the hours on the computer after your wedding that is spent sorting, touching-up and downloading the images and laying out your album. Oftentimes more time is spent on this aspect than is actually spent shooting your wedding.
I'm not telling you this to scare you but to let you know that when you hire a professionall there are many reasons that the cost is greater then someone down the street who works a full time job in an office and shoots weddings on the side.

Another thing that the bride and groom really need to plan out is their schedule, to make sure you have set aside enough time for portraits. Quite often when I talk to the bride and groom I'll ask them how much time is between the ceremony and reception. Usually there is about an hour and a half, most think that is plenty of time. When I start asking questions though that time disappears rather quickly. Are you doing a receiving line after the ceremony, and if so how many guests are you expecting at the church? This usually takes anywhere from fifteen to thirty minutes. Are you taking a limo run before you do portraits? Another fifteen minutes minimum. How long from the church to the receptin hall? Then there is trying to get all the family members together for their portraits. Did you want to go to another location for portraits? That could easily take over an hour! A certain amount of the time can be returned by doing as many images as possible before the wedding. Bridal portraits with parents and wedding party, grooms portraits with wedding party and parents can all be taken before the ceremony.
If you're not superstitious you can even do the bride and groom portraits before hand. I never push this but I do recommend it. The groom is more emotional when it's just he and his bride to be when they see each other for the first time, and it also eliminates a lot of the jitters.

Also decide how long you really need the photographer for. Most of the time I am asked to capture the reception images and I truly enjoy doing it! I get the entrance, the toast, the dances, garter/boquet tosses and sometimes even set up a mini studio to take portraits. After those events are covered though, all that's left to capture is 'candid shots'.

As for my pricing I've tried to keep it simple to make sure you are paying only for what you want, if you'd like to see what I charge it is available here:
http://www.sydneysstudio.com/pricing.html

Our purpose here is to help anyone with photography related questions. I have been shooting since 1974 and shooting professionally since 1997. We are open to most any questions you may have, whether it be about technique, equipment or the business of photography. It is also our desire to answer questions from people just wanting to know about how to pick a wedding photographer (or a photographer for any purpose). You questions can be general or they can be specific.
I have been using Photoshop since before they came out with the CS version. I feel qualified to answer basic questions on the usage of the software- but if it's really technical I will probably send you to another site.
We have been shooting digitally now for almost 10 years, in the event I can help you with any questions there. I do not generally recommend specific equipment but I will help you in choosing the features that are important.