Pretty good advice has already been given.
Some thoughts:
At the beginning, you might want to remove/detach any sway/ equalizer equipment on the hitch. (So you don't bend or break anything)
Talk to your helper and get your signals straight. Use hand signals directing the rear of the trailer. Point the direction, no verbal turn left/ right, no turn the the wheel rt/lt.
Helper needs to stand where THEY can see YOU in the side mirror. If they can't see you, you cant see them.
Helper needs to look up for tree limbs, down for posts, boulders etc.
Especially at the beginning, your helper needs to watch that you don't jackknife the rig.
Use phones or walkie talkies so you do not have to yell at each other. Set on hands free.
Hand on the bottom of the wheel and move it the direction you want the REAR of the trailer to go.
Keep the rig as straight as possible. Back and forth is OK, but move slowly, the rear of the trailer will swing.
It's easier to back if you have a reference point. Tree or wall is good. If practicing in a lot, put it in a specific space marked with lines or cones.
You took step one by asking for help! Where was the internet when I was learning?!
Norm
F1BNorm