Found this on a forum years ago, I've lost the info for original attribution:
Backing a 5er
There are a few tips that make it easier.
Tip 1: Do everything possible to insure that you will be turning on the driver side. Even if it means driving around the campground and up/down a few roads to get yourself turned around. Passenger is your blind side and should be last resort.
Tip 2: You have to learn how long the reaction time is for your trailer to react. Go to a parking lot and practice. Always use your trailers rear axle as the reference point. The reaction time is the time it takes from the time you turn the tow vehicle steering wheel until the time the trailer starts turning.
Tip 3: There are two terms you need to know. Neutral, Jack and Chase. Neutral position is when the tow vehicle steering wheel is at the position where the truck is going in a straight line. When you Jack the trailer you are causing it to turn the opposite direction that the truck is turning. Such as in jack-knife. Chase is when you are trying to straighten out the truck and trailer, thus the term chasing the trailer.
Tip 4: Get out and survey the parking area (with your spotter) for obstructions. Determine where you want the trailer to end up and pick a reference point, which will act as the "edge of the parking area".
Tip 5: Start with the truck and trailer traveling straight. You want the side you are turning into to be about 4' off the curb or edge of the road. When the tow vehicles rear axle is at the far edge of the parking space, cut your truck wheel hard away from the curb. When the truck is about a 45-degree angle to the curb (or as close as you can get given the space you have to use) straighten the wheel back to the neutral position. As soon as the truck has begun going straight, cut the wheel hard in the opposite direction until the truck is again parallel to the curb. STOP. Your trailer is now at a good angle to start backing up.
Tip 6: Jack the trailer until it get to about 15-20 degree angle of the space you are going to park it then start chasing it.
Tip 7: If your running out of space to get the truck & trailer running straight, don't be afraid to pull forward to help straighten it out.
Tip 8: PRACTICE, PRACTICE, PRACTICE, PRACTICE, PRACTICE, PRACTICE, PRACTICE, PRACTICE, PRACTICE, PRACTICE, PRACTICE, PRACTICE and never backup with out a spotter.
Other than the above the best I can offer is always use the same spotter. I watch the DW no matter who else if waving their arms at me!