Leather and snow aren't exactly friends, especially when you add in salt. So what do you do when the weather is bad and you want to protect your shoes? First and foremost, try to pick shoes with a thick rubber sole and avoid wearing nice dress shoes outside when the weather is bad.
Sometimes wearing nice shoes in bad weather can't be avoided. So the first step is to keep them conditioned! A shoe that's dry will soak up all that nasty salt and water and quickly warp, stain and crack your leather. A nice layer of conditioning will help repel that stuff from getting to cozy inside your shoe.
If you do wind up with salt stains, you want to take care of them as quickly as possible, before they have a chance to create cracks and warping. The best way to do that is with a solution of 50/50 white vinegar and water, or for suede, full strength white vinegar. Use an old rag to apply the vinegar solution to the leather and allow to dry. Depending on how much the salt has embedded into the leather, you may need to repeat this process a couple times. I recommend keeping a rag and vinegar solution in your car or at the office, so you don't have to wait until you're home.
Once the salt has been removed, it's important to get your shoes shined as soon as possible to restore the conditioning and eliminate dryness.