FWIW.
Training a system is key. IMO. I use the concept of tell me which way you want the rear end of the whole rig to go, be that a truck or truck and trailer. There is only one "more driver's (side)" and only one "more passenger's". Stopping if they get out of sight, or not, gives them time to process the spatial relational brain work (men are supposed to be naturally stronger in this, IIRC, so give them time. Had a friend's girlfriend refuse to back a trailer calling it Guy SHIT!) and translate it into words. Giving rough estimates helps me a lot more than come on back, come on back STTOPPPP!. 20', 15', 10', 8', 6' (stop and assess how much fine correction side to side), 5', 4', 3', 2', 1', 6", 4", 2", Stop. We connect almost dead on each time standardized way and standardized commands.
People say things that aren't standardized in ambiguous ways like "that's good" instead of "stop".
For a stick shift, parking slightly uphill is nice, allowing gravity to roll you backward toward your hook-up.
I've also had to instruct people to use two feet while driving an automatic for control. The key to log riding on a mountain bike is to pedal and drag your rear brake. It give more control in some situations, and prevents sitback on some hills.