Pick up two orange traffic cones.
Go to an empty parking lot and place the cones at the back of a lined parking spot and practice, practice, practice.
One real important thing I was told when I was a newbie that made ALL the difference is to always approach your site where you are backing in on the drivers side. So you are using your side mirror NOT the passenger side mirror. All that takes is going around and coming in from the other direction. You will be shocked what a difference doing this small thing makes.
And those two orange cones? KEEP them on board. When you go camping place them at the end or your site on either side. You will never need another person to help you back in ever again. You will see where the end of the site is and where to stick your RV between the cones. No yelling waving hands spouse, walkie talkies needed!! :C