Can’t believe I’ve been driving for over a decade and never knew how to properly set my mirrors. Here is the gist of it:
To adjust your mirrors properly, put your head against the left side door glass, then adjust your left mirror OUT until you just barely can (or barely can not) see the side of your car. THEN, move your head to the center of your car and adjust your right mirror out until you can barely (or barely can not) see the side of your car. The goal is to set it up so that once a car leaves your REAR view mirror, it appears in your SIDE view mirror – and once it leaves your SIDE view mirror, it appears in your side window/peripheral vision. Unfortunately, some American cars don’t let you adjust the mirrors out far enough to completely accomplish this. I recommend experimenting in a parking lot until you get the ideal angle.
CarTalk covered this a while ago and it’s worth sharing (their page has graphics available in the downloadable PDF.) Might as well get used to using the mirrors correctly now, before I’m an old fart and can’t easily look over my shoulder.