another backing tip-set yourself up for success.
If you have to back in on a slight curve-like backing into a campsite from the road-go forward farther than you think necessary. give yourself plenty of straight back backing before you gently start the curve. also, when you initially pull forward, angle the tow vehicle and trailer to the opposite side of the turn. this gets your rig started in an angle that will help and make the turn less sharp.
WE take people to an empty school parking lot and practice backing-it really helps you get the feel of doing it competently.
as mentioned, a spotter always helps. Laura uses hand signals-pointing which way the trailer needs to move. sometimes she can stand where we want the driver's end of the trailer to be. This gives me a target to work towards.
Vann