Buy time to react
Parking lots are filled with obstacles and hazards, but often the biggest danger is other drivers. They may cut across empty rows, drive too fast, or ignore signs and pavement markings, endangering everyone in the lot. The best way to deal with these drivers is simple: Slow down. This buys you time to react and avoid a collision. Be especially cautious when turning corners and backing up.
Parking lots are full of people coming from and going to their cars. Though pedestrians may not be looking out for you, it's still your responsibility to look out for them. Keep a wary eye out for any pedestrians who may cross your vehicle's path, and be sure to obey all crosswalks within the parking lot. When entering particularly high foot-traffic areas, take your foot off the accelerator and cover the brake. Anticipate pedestrians even if you don't see any. If you're in a busy shopping area, remember that people lugging sacks of groceries or other purchases could also be shepherding hard-to-see children, too.
Door dings and scratches are aggravating and hard to avoid. No matter how courteous and conscientious you are when parking, you can fall victim to someone else's carelessness. One way to reduce the risk of door damage is to park away from other vehicles. This may be inconvenient, but it's considerably more polite than parking your vehicle across several spaces to keep others from parking near you. And the extra walking is good exercise.