After 25 years of pulling our little boat, and a small trailer we use to haul trash, I have gotten reasonably good at backing a trailer. As already said, go slow at first. I can offer a couple of tips that I received when I first learned that may help. A lot easier to show you than tell you, but I'll try. I use the top of the steering wheel instead of Stephen's method (but really the same thing).
First, if you have the room, the easiest way is to pull forward until the trailer and vehicle are in a straight line and pointing in the direction you want to go when you back up, so you can back straight in. Practice this first.
Pull forward and get lined up. Then:
Look in your side mirrors, if it's a short trailer you may not be able to see the trailer at all, this is ok. If it's a longer trailer then you will see equal amounts of trailer in either mirror. Put either hand (whichever is comfortable) on the
top of the steering wheel. Start to back up. Everything will go smoothly for a few feet, then the back of the trailer will start to come around on you to the left or right. Lets say it comes around to the left. You see the trailer in your left mirror. Move your hand (that is on the top of the wheel) toward the left -
see the trailer, move your hand in that direction. Don't let things get too far - you need to correct at the first sign of movement, and make small corrections. So you have corrected, but probably a little too much. After a few more feet you see the trailer in your right mirror. move your hand to the right to stop it, rinse and repeat. The backing process ends up being a series of gentle s-curves in the general direction you want to go. If you correct soon, and don't over-correct, the s's are almost imperceptible. If things get out of hand and the trailer starts to jackknife, pull forward and get lined up again.
The other situation is when you don't have enough room to get straight, and have to back around a curve. Most common is backing into a driveway from an intersecting street. You will use the same trick, but in a slightly different way. I have attached a little diagram that may help. For my example, we assume you are coming up the street and the driveway is on your left:
Come down the street and pull past the driveway - the car and trailer should both be past. While you are still going forward, swing around to the right. This starts to get the trailer's back end pointing to the left, where you want it to go. Look at diagram #1 - the trailer is starting to point in the correct direction, but if you started to back up you can see the trailer would just back up the way it came, into the street. So, at the last second, just before you stop, crank your wheel hard to the left. Now the back end of the trailer breaks to the left, and the car and trailer are both pointed in the correct direction, so when you back up it will naturally want to head for the driveway (diagram #2). Practice this a few times - getting the trailer pointed correctly and the angle between the car and trailer is important. Get out and walk around to have a look if you have to.
Now you are ready to back in. Take a second to look in your left mirror and get the picture. You want to maintain this picture until the trailer is lined up in the driveway. Start to back up. If the trailer starts to swing more to the left, move your hand to the left. If it starts to straighten out, moving to the right, and you see less trailer in your left mirror, move your hand to the right.
Once the
trailer is almost straight with the driveway, you want to bring the car around so that you end up with car and trailer straight. Same trick. Since you want the car and trailer straight, and you are seeing the trailer in your left mirror, move your hand to the left. Not much. Just turn the wheel until you see the trailer begin to straighten out, as you continue to back things will straighten out.
Again, if things are getting out of hand, stop and pull forward a little. As you do, think about where you want the
trailer's back end to point, and steer the car to accomplish that.