For this to work with precision, it needs to be carried out as slow as possible.
As Slow as a Tortoise would be nice figuratively speaking.
If it is carried out slowly, it has the benefit of keeping the area around the car safe, as it will give you time to look around throughout the manoeuvre.
It will also allow you to correct any error of judgment during the procedure. If you go too fast you will run out of space too quickly, will not be able to carry out effective observations and could potentially lead to either hitting someone or something.
When you start learning this it is advisable to practice using a "Datum Point". Over time you won't need to use this as you become comfortable with your abilities and the cars capabilities, but to start with it may help you.
Looking at the processes below, once you have found your datum point STOP THE CAR from moving. This will mean that you can start from a tiny speed rather than the car already having momentum which usually leads to turning in at the wrong point or running out of space to complete the manoeuvre correctly and requiring a shunt to correct it.
Therefore if you are driving forwards into a bay to your left, get the car as far to the right of the lane you are in prior to turning the car into the bay.
Likewise, turning into a bay on your right, get as far over to the left of your lane as you can before turning in.
This will give you the maximum amount of turning / correction time before entering the bay.
Remember, if you don't manage to make it into the bay on your first attempt, just reverse out, adjust the position of the car and try again.
During your driving test, if your need what is referred to as a "shunt" (reversing the car out to have a second attempt) your are permitted to do this, and as long as this is carried out with control and effective observations throughout then a standard drivers fault will be recorded, not a fail.