If the wedding is taking place indoors, you should find out what the church allows. Many churches do not allow flash photography at all. If that’s the case, use a tripod, and set your camera to a slower shutter speed. This will assist you in bringing in as much light as you possibly can. Some churches also don’t allow for a lot of movement so you will have to set up in one place.
If you are allowed to use flash, use the three-light setup. The three-light set up means that you will have your main light focused on the subject from the front and a backlight on their backs. The main light should shine from above the subjects.
Finally, a fill light will be used to lighten up any shadowy areas and should be positioned opposite of the main light at a slightly lower angle. Check with the light meter to ensure that the light is adequate.
If you cannot set up your lighting, you should use the reflector. Try to bounce the reflector off of a ceiling or wall that is light colored (white, beige, etc.) as opposed to a colored surface. The colored surface will add that color to the photograph itself. You should also try diffusing the light if it is too harsh. Use a flash diffuser or sheer material to create the desired effect.