Checking for other cars and pedestrians
When you are parked in a space in a parking lot with cars parked on both sides of you and in front of you, backing out of the spot can be pretty tricky as well as potentially dangerous. You are at risk of hitting a car or pedestrian that is passing behind you. Obviously, that is something that you will want to avoid at all costs.
In order to be sure that there are no pedestrians or cars behind you before you start backing out, you should start by checking over both of your shoulders for cars and pedestrians that are directly behind you as well as for those that might be approaching from either side. If there are no cars or pedestrians coming, you can then put your car into reverse.
While you are backing out, keep checking over the shoulder that corresponds to the direction that oncoming cars closest to you might be coming. This will almost always be your right shoulder. Once you are backed out enough that you can see through your driver side and passenger windows, stop and take a quick look through each. After that, complete backing out while still checking over your shoulder. Only look forward once you have shifted your car into drive.
Backing out safely
When you are backing out of a parking spot, always do so slowly, cautiously and incrementally in case you need to stop quickly to avoid a collision. Other than that, backing out of a parking spot safely hinges mostly on properly checking behind you before and during the process. However, you should also check under, behind and on the sides of your car before you even get in for children, shopping carts and other potential hazards. You might not be able to see those things by simply checking over your shoulder due to their close proximity to your vehicle as well as their short height.
If you have a backup camera, make use of it before you backup. Do not use a backup camera instead of checking over your shoulders though. A backup camera will only show you directly behind you and will not give you a peripheral view of any kind whereas checking over your shoulders will. This will allow you to easily spot oncoming cars and/or pedestrians.
Backing out of a parking spot in a crowded parking lot can be both nerve wracking and dangerous. As a result, you must be as careful as possible. This will include checking the perimeter of your vehicle before you get in, checking behind you prior to reversing, reversing at a very slow speed and making constant over-the-shoulder checks as you reverse.