Many photographers now use the LCD screen on the back of digital cameras, as a final judge of whether their exposure is correct. Take a photo, check it looks all right on the screen and you're ready to go. The introduction of LCD screens has meant that sales of handheld light meters, which previously all serious photographers used to own, have plummeted.
I still may use a light meter, they are a superb tool to have in your camera kit bag, it’s great fun to use, increases your skills and can help you understand what he light is doing, I must admit, I have used a light meter many times when photographing weddings in the past, it taught me so much about light and how this affects the exposure.
However, just using the LCD picture as a guide to whether your exposure is correct is fraught with problems. Firstly, if you look at the same picture on the screen outdoors on a bright sunny day versus indoors in the shade, there's often a big difference. Also, many photographers have their screens set to auto adjust to the surrounding brightness levels, so it can look different minute to minute. It's impossible to calibrate your LCD screen in the same way you can your computer screen. All you can do is adjusting its brightness manually. It's good practice to take a photo, then load it onto a computer with a calibrated screen. Put the memory card back in the camera, then adjust the camera LCD brightness until it's as close to the screen as possible. It's slightly more accurate than the auto mode, but of course a bright day outdoors really affects how your eyes see the screen anyway. As standard, many camera screens seem to come pre-set at a very bright level. (Cynics might say this is so that when you try it in a camera shop, it looks impressive.) A far better way to check exposure is to check the histogram, which essentially is a graphical representation of the tones in a photo. What you're trying to avoid is the graph either clipping off the right or the left edge of the screen. It's pretty technical, and many photographers set their screens to check out separate histograms for separate red, green, and blue channels. There are whole books written on the subject, and it can be good practice to learn how it works. In reality, when in the field and busy shooting, many successful photographers find this method a bit too technical and fiddly. If you think this would be you, then one of the best ways to see if your exposure is right is to activate your camera's highlight warning. Set like this, any overexposed highlights in your photo blink very obviously; this can ensure you keep the important details in the brides wedding dress.
It's always good practice to avoid blowing these highlights, as once detail is gone, it's gone, but you can often pull shadow detail back. Knowing if your highlights have blown allows you either to adjust your camera or flash to underexpose a little, or understand that you'll have no detail in the final shot. This may be what you want, (in a high-key shot, for example), or it may give you a vital warning you've just overexposed a bride's white dress and allow you to reshoot. Either way, the blinking is an obvious visual cue that works if you're in bright sunshine or indoors in a darkened room. A final parameter to consider is the camera's white balance. Auto can work well, as long as you're shooting in Raw and there are no mixed light sources. A better bet is to manually set the white balance using the built-in settings.
Choose the white balance to suit the main light on the subject, more often than not flash if you're using strobes. A better alternative is to use a calibration target, such as the X-Rite Color Checker Passport, to make a custom white balance setting however this can be a tad difficult when you are the official photographer at a wedding.