Fog and mist add a lot of atmosphere to a photograph but they can make it a bit tricky to get the exposure just right. The problem is that both fog and mist reflect a lot of light and they fool the meter into thinking there is more light than there really is, so if you expose at what the meter says, you get an underexposed (dark) photo. The situation is really easy to solve using your exposure-compensation feature. Typically dialing in a setting of +1 stop or even +1.5 stops of exposure will give you a well-exposed fog shot.
If your camera has an automatic exposure bracketing feature you can use that to take a burst of several exposures, each at different settings. You can set the bracketing feature to automatically take a series of three (and, on some cameras, more than three) exposures in user-selectable increments ranging from 1/3 stops to 2 full stops. A typical sequence (in single stop intervals, for example) would be: -1 stop, correct exposure, +1 stop. Then you can choose the best exposure later. Bracketing is a great feature that I use often, but it works best on a tripod where you know you're getting the exact same framing for each shot.