It’s harder than a trailer and car imo. Keeping it slow is the key. Then you can make corrections as you go. Try it in an open field with a couple of cones and just keep practicing until you get it (assuming you know the correct technique).
You label one hand 'bend' and the other 'straighten' and that helps. Except, you start with the opposite. So, I get it going, then label one bend and the other straighten. To get it going is only slight though.
I would start in a large area, turn the wheel one way then as soon as the trailer is slightly off, feel which hand bends it and which straightens it.
Most people bend it far too much to start with, once it is bent too much no amount of twinning the wheel will straighten it again, you need to drive forwards to get it all ready to start again.
Do it slowly, don’t oversteer, go just a couple of feet before stopping and assessing if it’s going the right direction. FWIW I tow a lot and I’d rather drive our Isuzu pick up with the 12’ trailer on the back around our narrow country lanes, reversing all the time, than reverse the bloody quad and poo picker onto the muck heap! Single axles are so much more difficult!
I find it easy to reverse my jeep and 511. But the quad and little trailer at work I have no chance! I can almost get it out of the yard which is a straight back and turn but that takes a while it just all seems to happen so quick. I find it hard to get the quad to move smoothly which Is the problem. It seems to rev and rev and then fires off. I have the same issue going forwards with it too. Is this a quad thing or so I just not drive it enough to master it?