Learn to back with mirrors. Pick one mirror, preferably the drivers. If you can’t see the trailer, get a couple of markers on poles and attach them to the rear of whatever you are backing. Pick a line you want to stay on until you get the hang of what’s going on behind you. I say choose a mirror because if you look from one side to the other you will end up over correcting. Truly the shorter the tongue, the quicker it will turn. Watch that drivers mirror and as soon as you see the trailer starting to move either direction, turn the steering wheel toward what you see. If you see the trailer in your left mirror, turn left. Try to make adjustments small and go slow at first. If you can’t see the trailer in your left mirror and you glance to the right and it’s there, turn the wheel right. The back of the trailer will go the opposite direction you turn the wheel but in this way you will get to where you won’t even think about it. The most important part is to stage the truck and trailer straight. Let’s just use a boat ramp for an example. To get your trailer straight you will drive past the point you want the rear of the trailer to end up at. Then you will crank the vehicle sharp to the left. You can actually see the rear end of the trailer react. Then crank it back to the right until you are sitting square with the water. You now have better control of the trailer. I have backed semi trailers on curvy roads. Like they have all said, it just takes practice but use a method you don’t have to think about what you are doing. Aim the nose of the truck in the direction you see the trailer if it starts getting out of position.