There is a simple solution to this; set your exposure to +2/3 WHEN the bride is in the picture. Don’t forget to dial your expose back to normal when taking pictures of only the groom (in fact, you might want to go -1/3 exposure in these situations) or of the guests.
Other things which can screw up your exposure are:
- Reflections of the sun on objects (try to find something to block the reflection)
- Bright lamps/lights behind the scene. (try to find something to block the reflection)
- Bright Windows in the frame. (increase exposure by 1+)
- Mirrors and your flash (try to move so something is blocking the mirror)
By keeping this all in mind, you are more likely to get properly exposed pictures without having to photoshop them later.
Another important thing to do, regardless if you think you are sticking the exposure or not, is to take your pictures in RAW format. Although the extension and software used to manipulate RAW images differs from camera to camera, raw images offer a much broader latitude in changing the exposure settings. Where a JPEG might be able to be manipulated +-1 stop, a RAW image can be manipulated +-2 stops due to it containing much more meta information and it being a 16 bit image. Most cameras which shoot in raw ship with software allowing you to manipulate raw images.