Many of us have had a close call or two from not being able to see what is in our blind spot while driving. Traditional wisdom recommends you adjust your side view mirrors until a portion of the door of your car is visible, figures 2 and 5 below. Notice how the red car is completely out of the field of vision.
The Society of Automotive Engineers have a better way. They recommend you adjust your side mirrors until there is only slight overlap between their range of view and the view in your rear view mirror, figures 1 and 4 below. This eliminates the blind spot on the driver’s side, and takes advantage of a wider field of view on the passenger side rather than duplicating what you can already see in the rear view mirror. Cars coming up on either side show up in the side mirrors as soon as they leave the inside mirror. Adjusting to the new angles is disorienting for some drivers and takes some getting used to, but eliminating blind spots makes for a safer ride and reduces the need to look over your shoulder for lane changes.
Source: Car and Driver