I've just given this exact same reply to someone else...
Practise, experience, and more practise. When you reach a level that takes you well beyond the basic level of a driving test, then even though your standard may drop on the day you will still be good enough to pass. It's up to your instructor (and yourself) to reach that standard.
When I was an ADI, 60% of my pupils passed on first attempt, and I rarely took someone for test more than twice because I made sure that they were better than 'learner drivers' when I took them for test.
If you keep failing tests, perhaps you need to consider whether your driving instructor is the one to take you to that standard?