We always suggest that you go to a school or church parking lot(when not being used) that has parking places/stripes to work for. There should be plenty of room to maneuver and practice. Pick out a particular space and try to back into it. Start big and get better(closer to the line) as you get better.
There are lots of hints and tips-where to hold the wheel, when to turn the TV, etc. this is what you might find on You tube.
The best advice i can give you is to set yourself up well in advance of where you need to turn when backing. Give yourself more room than you think you need. It is much easier if you can start off backing straight and then start the turn. Every vehicle is different with their turning radius, wheel base and steering. practice, practice and don't get discouraged. Nobody is born knowing how to do it. We all had to learn and practice.
We find it very helpful for Laura to be the spotter and give good hand signals--non-verbal communication so there is no yelling or screaming!! Talk with your spotter and decide what each signal means-remember that you are looking in a mirror and most things work backwards from what you expect initially. also make sure that you can communicate what the spotter is trying to get you to do. It helps if the driver gets out and surveys the area and has a good idea where they are trying to go.
good luck and patience
Vann