best thing to do is apply a good amount of wax before winter. hit the local car washes atleast once a week depending on how much salt/snow you have been driving on. a good spray down is better than nothing. if you have access to a garage about halfway through winter i would clay bar the car and wax it again...
thats just me tho im pretty "anal" about my car lol
Before the winter, I would give it a great detail job... I do this twice a year.
Wax - 1st layer of protection
Wax - 2nd layer of protection
Seal - 3rd layer of protection
I'd also invest in a cover... I take mine on and off every day and it helps protect the ride quite a bit... from the tree leaves to bird poops... it makes a big difference in how many times the car needs a wash!
Instant detail it between washings and get a good pair of gloves... LOL