Even with the rash of new sensors and driver assistance technologies in cars lately, a piece of glass the size of your hand remains the best technology for knowing what's alongside your car and not merging into it. Here's the admittedly non-intuitive way to adjust your side view mirrors to do that job.
Adjust your seat. (See our other CNET how to to get that done easily.)
Lean left. Put your head almost against the left door glass. I know it seems weird, just do it. Now set that side mirror so you just see a sliver of that side of your car.
Lean right. Put your head about where the center console is adjust the right hand mirror to just see a sliver of that side of the car. .
Check it out. It may seem odd at first, but get on the road and notice how wide the view is across all your mirrors. You're probably seeing much more of what's behind you, yet with enough overlap between the mirrors that you won't miss anything in a gap. The way you used to adjust your mirrors probably had a lot more redundancy - and blind spot - between them.