Final answer:
When backing up a vehicle, the best practice is to back up slowly, look over your left shoulder, use mirrors, and only sound your horn to alert others if necessary for safety.
Step-by-step explanation:
When backing up, the best practice is to back up slowly and look over your left shoulder to ensure a clear path. Additionally, using your mirrors is important, but they are not the only tools you should use; your direct line of sight is equally critical for safety. It is not advisable to sound your horn while backing up unless it's necessary to alert someone of your movement and prevent an accident. Safety is critical when operating a vehicle, similar to wearing appropriate safety gear, like helmets, safety belts, and protective eyewear, during various activities to prevent injuries.