My advice about backing is to avoid it when possible. I use to train guys to drive tractor trailers and saw several accidents were guys were backing when there was no need.
If you have to back in, try to back in on the driver's side instead of blind-side backing.
My dad drove trucks for 50 years and told me if you have any doubts about getting in and out of a place, always back in and drive out. Better to not be able to get into a place than to get in and not be able to get out.
When backing get as straight as possible before you start. Give yourself more room than you think you need. Put your hand on the bottom of the steering wheel and move it in the direction you want the trailer to go. Try to make small inputs and don't cut the wheels any sharper than you have to. If you get behind in your steering, pull out and try again.