How to adjust your mirrors correctly:
Your interior mirror should be adjusted so that you have a fairly central view of the road behind. Sometimes a bias slightly to the right improves the perspective, and gives a better view of potentially overtaking traffic. In the photo the centre of the rear screen (silver sticker)
lines-up with the centre of the night dip lever on the mirror itself.
Your door mirrors should be adjusted (as shown) so that you can see a little of the side of the car. This is so that you know where anything you see in the door mirror is relative to you. The horizon in the door mirror should be about two thirds of the way up.
Each side of the car there are blind areas, areas that you cannot see when you are looking forwards, and that you can't see when you look in the mirrors. A car about to pull away on your right, or from a driveway, can easily be hidden in your blindspot.
Also please don't change these settings for your drivng test as the examiner is trained to look at you at the correct times to see if you are looking in the mirrors. If you adjust them off-centre, you just won't be able to see correctly. this is because after driving for a while on your test you will forget to move your head, and just accept a poor view. The best way to safeguard yourself for your test is to look in the mirror at the correct time.