Get a allingment with zero camber in rear so all tire is touching the floor
Better tires for the snow/rain(no all season crap)run this tire on separate wheels so you can switch in summer real easy wider tires do help but you can go only so far
Weight always helps but not to much......cause u will hit the brakes and the rear end will want to flip around
Down force would help but if ur car looks stock then u would look like a Ass
Softer setting(or stiffer depending on weight) on suspension that works with the weight that u used for the rear
Try A Apache helicopter with a flamethrower in front of it to blow all the snow and ice and water away with chuck Norris flying it so the jobs done right tehe
