I learnt another way...I always had blue tack in the back left window and when the back of the car (one in front that I was parking behind) reached the blue tack, aka the back corner of the window, one turn to the right, then reverese, then when the back of their car was in the middle of the front passenger window, one turn to thr right, then looked out the passenger mirror and when you could see their handle 'resting' on the pavement, another turn to the right and carry on reversing.
I liked that wasy because there wasn't really any of your own judging involved...when the car was at the blue tack, you turn!
I'm quite short though and I always moved the seat miiiiles forward and never realised I couldn't see out the passenger mirror, I finally passed my test when I moved the passenger mirror as well as when I moved my seat and I could see out of it so I could see the kerb!!