The first step is to adjust the rear-view mirror to do exactly that - give you a view directly to the rear. Position it so that it best covers your view straight out the rear window. Don't bother tilting it to one side or the other to assist with your view of traffic to either side of your car. That's what the side mirrors are for.
Next, lean your head until it almost touches the driver's side window. Then, adjust your left side mirrors so that you can just barely see the side of your car, and no more than that.
Lean your head to the right towards the middle of the car and adjust the right side mirror so that you can just barely see the right side of your car. You should NOT be able to see the side of your car when your head is perfectly upright. After all, why would you want to? When was the last time your own car ran into itself?
Check for blind spots by doing the following: While driving along a four-lane road in the right lane, note a vehicle in the left lane coming up to pass you from behind. Without moving your head, glance in the rear-view mirror and follow it as it approaches your car in the left lane. Just before it disappears from your view in the rear-view mirror, glance to the left side mirror. There it is. Now follow that vehicle in the side mirror as it begins to pass you. Then, just before it disappears from the side mirror, you should see it with your peripheral vision. Notice that without even turning your head, you never had a blind-spot. Then try it with the right side mirror. Watch as you pass a vehicle travelling in the right lane go from your peripheral vision, to your right side mirror, to your rear-view mirror. Again, no blind-spot. If there is a blind spot for even a fraction of a second, your side mirror adjustment needs some fine-tuning.