After thirty+ yrs ot towing multiple trailers, did not know all these "money wasting" gizmo's to help one back up to a ball were available.....
"PRACTICE", then again, many of us do not have jobs that require us to hook a trailer of different types up daily either. But as mentioned, know the rough how wide to each side of the truck in the mirror's to be, even at an angle you can learn this same technique. I really PO'd a client as I backed up to my equipment trailer and put a pintle mount on in the first shot, blindfolded using my dumptruck and side mirrors only.
05 Chev CC D/A LS Dooley
92 Navistar dump truck, 7.3L 7 sp, 4.33 gears with a Detroit no spin
00 Chev C2500, V5700, 4L80E, 4.10, base truck, no options!
92 Red-e-haul 12K equipment trailer
3 Single axle utility trailers
I used a screw used to hold the bedliner in my tailgate to "aim". I align the screw with the trailers jack and back up slowly until I feel the hitch ball contact the hitch. Then, I pull forward a few inches. I can backup correctly in 1 to 2 trys.
A sticker or mark on your tailgate is all you really need.