Backing up a trailer requires extensive skill and precision that isn't necessary when driving a car in reverse. Whenever possible, it is best to back up a trailer with the help of a spotter. It can be done solo, though it will require taking extra precautions.
When attempting to back up a trailer with a spotter, you must first establish some hand signals you are going to use. You can't assume that the hand signals for backing up a trailer are universal. Though many of them are, if either of you are new to the process, there will likely be some confusion. Establish hand signals for left, right, forward, backward, slow down and stop.
Position cones where you want the trailer to end up. This will give you a better sense of the direction to guide the trailer. Have your spotter stand a reasonable distance from the front of the vehicle, so he can see on both sides of the trailer. As you are backing in the trailer, make sure to keep the windows down and the radio off so you can hear any warnings or directions he is unable to communicate through hand signals.
Back up a trailer with your hand at the 12 o'clock position. Turn the steering wheel in the direction that the spotter points. Don't make sharp turns, as you may jackknife the trailer. Move the steering wheel slowly, while you gently press the gas.
Attempting to back up a trailer without the help of a spotter requires taking extra precautionary steps. Before beginning the process, thoroughly scan the area for any potential hazards, such as animals, children and low lying branches. These are the things your spotter would normally be able to notice.
Always back up from the driver's side so you can see the direction your trailer is heading. Backing up from the passenger's side is very dangerous as there are many blind spots. Keep your window down so you can stick your head out to get a better view of the progress you are making. Consider the direction you want the trailer to go and mark a path. Place large orange cones along the path, on the driver's side and follow the path of the cones using the mirrors.
Place your hand at the 12 o'clock position on the steering wheel. Guide the steering wheel gently in the direction you want the trailer to go. To play it safe, periodically get out and check your progress to make sure you are heading in the correct direction and verify that children and animals haven't entered the area. Over time, you will find it becomes easier to back up a trailer.