You need PRACTICE, trial and error to improve backing. 1/2 time DW is my spotter and we communicate quietly via cell phones. The other 1/2 of the time, alone, I use 4 orange caution cones and pace it off. The last cone is at the driver door! That is MAX I can back up. No cameras. No CAMPGROUND HELPERS; turn your wheel this a way; no, the other this a way 😩. Usually I have to exit the truck 2x to assess alignment.
I did learn a few tricks: never use slider unless situation is impossible;
Always remember the 5er only turns when it has slow steady momentum; simple steering is better than aggressive; shut off your trailer brakes when backing. You do not need them.
Try to practice when you can and confidence quickly builds. ALWAYS assess your surroundings for obstructions BEFORE backing, not, ut ohhh!! 👍