You MUST use your internal mirror before you slow down, before indicating, and before pulling in or out. As a reminder use it every 5 seconds, every time you change gear, and every time you see a hazard ahead. Before you move to the left or right you also need to use your side door mirror, also before you turn left or right. On test check your mirror twice every time the examiner gives you an instruction.
The simplified sequence is:
Mirror (internal); Signal; Mirror (side); Manoeuvre
The importance of using the mirrors correctly cannot be stressed enough. With practice you should be able to use the following advanced sequence for enhanced safety and to impress your examiner:
Mirror (Internal + Door)
Signal
Mirror (Internal + Door)
Change position or lane
Mirror (Internal)
Change speed (slow down)
Mirror (Internal)
Change gear
Mirror (Internal + Door)
final turn or movement
Mirror (Internal)
Accelerate away
Check your mirror before you do anything at all, and then frequently as you do it, and then afterwards.
Just remember to check the interior mirror before doing anything at all, then check the door mirror before moving to the side or turning.