Wash your car regularly - I'd recommend to do this at least once a month. Things like bugs, bird's dropping, or limestone dripping do harm to the paint leaving permanent stains if not washed off in time. When the car is clean, all the moisture dries up quickly, but when it's dirty, the moisture accumulates in dirty areas causing corrosion. At least once in a while use pressure wash - it removes the dirt from difficult to reach areas (I do this at a coin car wash stations). Wash off all the places where the dirt and salt might be accumulated; for example, behind moldings, inside wheel arches, under the bumpers etc. It's particularly helpful after winter - to wash out all the salt accumulations that speed up the corrosion process. Most of car wash stations also have optional waxing - for example, at coin wash stations this mode calls "high pressure wax". I do recommend to use this option, it's not only makes the car shiny, it helps to protect the paint.