Lots of good ideas, this is what worked for me.
Pick the one you like best. Like most things, it takes longer to explain it than do it.
One step at a time. “Go slow and your get in trouble slow”. Meaning you will have time to see if you are going to hit something. Also get out and look, couple times if you need to.
The two basic moves will be straight backing and backing while turning.
Side mirrors only, a thin slice of your truck anchors where your looking. It will be easier to use and turn on your left side at first.
You want to be able to see the side of your truck, trailer tires, line or spot on the ground (much like the sight picture if you hunt.) All lined up.
Straight backing. Go to an empty parking lot with lined parking spots.
Start with rig straight lined up with the site (parking spot).
Pick an edge of the pad, clump of grass, line or seam in the asphalt to use to line up with. At first just pull forward without turning the wheel then back up without turning the wheel. Do it several times. Goal is to see what your tires do next to the line, try not to cross it.
Your goal is to use your mirror to see the trailer tire slowly stay next to the line but not cross it. Keep the tire a few inches from the line as you back up and pull forward. Go slow and see it.
Go slow. Use hand at bottom of wheel to free your brain. (Hand moves a little right - back of trailer moves a little right). Small movements, which is why its best to start straight, then learn turning while backing.
Practice straight backing with a line next to your tires. Imagine a line if you need to but a real line will make it much easier.
When you pull forward, notice how far your trailer tires are from the curb, line, seam or edge you picked out. Look into the mirrors, drive back and forth until you understand how the steering wheel movement moves the trailer. Remember when turning, the trailer tires will turn inside your truck. This means if your turck tires just miss the curb, your trailer tires will hit it.
You have to keep your truck a little farther out but see the trailer tires as they turn around an object or mark in the road. Once you see how the trailer turns going forward, use that to learn to back while turning.
When you learn your turning radius, you will be able to pick a spot like a crack in the road, clump of grass, oil stain and be able to turn around that mark as you back up. If it disappears in your mirrors stop and find it again by moving forward then try again.
This is all practice before you get to the RV park. Make it fun in a parking lot.
You will get it, we all did at one time. Cheers.