As a wedding photographer Chicago couples refer, I usually begin working with the bride hours before the ceremony starts. Most brides will be getting ready at a nearby hotel or family member's home, large enough to accommodate all the bridesmaids. Since most weddings take place during the day, there should be plenty of available light in the room to work with. Natural light will always be stronger as you get closer to the window. You'll need to evaluate light from this window or windows in different parts of the room. We know that digital photography doesn't allow for over exposing the shadows so you'll need to blend the light with a proper exposure.
Window light is very directional too so your exposure will vary several stops in different parts of the same room.
One thing to keep in mind is to avoid having the window as the background, unless you are creating a silhouetted image or can use a reflector, which I'll address a bit later. If you shoot towards the window, you may get a proper exposure of the subject but the background can get washed out. Window light can be very soft and flattering for facial features. Many stylists actually face the bride towards the window when applying makeup so your job will be easier.
Shooting with a long 2.8 lens will allow you to sit in the background and capture the day's events. The long lens will help eliminate some of the busyness of the background too. Hotels are famous for warm lamps, busy patterns and artwork. Zoom in a bit tighter on your subject and the soft light coating them. Don't be afraid to use a monopod, that way you can get the slowest shutter speed needed and stay mobile while your subjects are moving around the room.
When the bride is dressed and ready, window light will help you create a nicely lit portrait.
A reflector or bounce card is a good thing to carry for just such an occasion. While you can use these for gathering the candid moments, it defeats the purpose since you will be shining light on your subject and possibly distracting them. Try having your bride stand near the window and gage the light and composition. If the light is too harsh back up, metering only the wedding dress and skin tones. Direct sunlight will be difficult to work with since it creates heavy shadows on the face and will cause the subject to squint. Avoid direct sunlight by closing the window shears that will diffuse the light and make it more even.
To avoid having a harsh shadow/highlight situation, use the reflector or bounce card to fill in the shadows. You can also use it as a kicker light by positioning it behind the subject. Harsh shadows and highlights can make some images look interesting but you'll want nicely lit and balance portraits too. Keep in mind that as the day goes on, light gets weaker.
It may not be shining through the same window by the time your subject is dressed and ready. It would be nice to have as much time as you need but that's usually not the case. A good wedding photojournalist will scope out other rooms and window lighting and plan ahead. Once you find the right combination of window light, reflector and background, get to work. And don't forget to bracket!