Best Ckr
Try to keep your head and eyes moving to watch out for the dangers, but remember it's like shooting a gun keep your eyes on the "site".
If you are trying to back up to a dock either aim for the yellow line, the dock bumper, or anything else.
But remember there are 2 mirrors, aim for the same thing on both sides.
But the best thing is what works for you. Drivers with 30 years have trouble from time to time.