Get an 18 grade grey card when shooting in locations with snow, maybe water, sand. Meter off of that to get the proper exposure. The texture in the snow will be noticeable. Or just meter off something dark, such as your hand or a tree.
if you're shooting film, bracket your shots (look it up)
if you're shooting digital, look at what your results are as you shoot, and make adjustments as needed.
grey cards are always a good thing to have too.
i'm guessing if you're asking general questions like that though, you probably don't have a camera with much in the way of manual control.