Adjust the Exposure
Snow is actually brighter than the camera's exposure records it. To make your snow look pristine white, lighten the exposure but keep texture in the brightest areas. You can do this by using the Snow (or Beach) scene setting. Or you can set the Exposure Compensation to +1 for snow in direct sun or +1.5 for snow under overcast skies
The most controlled method is using spot metering to measure the light on just the snow. (You will still need to adjust the exposure.) If your camera can display a histogram (a graph of the brightness in your photo), check it as a guide to an exposure that's brighter but not too bright. The graph should be shifted toward the right side instead of being in the middle. You can also practice on white subjects inside to figure out how much to lighten the exposure while still keeping important details.