My boss always caught me when I had the fuel truck. I had to learn how to steer compressors using the center mirror and watching the raincap on the exhaust as it stuck up above the fuel tanks...
Always pull up until the tractor and the trailer are in line...Practice, practice, practice...
As a driver trainer, I'd get kids from training schools. I'd take 'em to our rail to truck yard and have them back down between two rows of railroad cars that were not parallel. They would constantly swivel head between both mirrors until I stopped them and had them look at their tracks in the dust...looked like a snake was slithering down the roadway! Got them to focus on one side mirror and occasionally check the other side and the tracks got alot straighter...Practice, practice, practice...