@martin
by being brutally honest with yourself and asking if you are just guessing or know the underlying principle/law etc.
the aim isn't to memorise the questions, it is to identify what areas you are knowledge deficient is. I'll admit it takes a certain amount of emotional maturity, to be honest with yourself about your knowledge, but then again so does flying a plane.
Once you get a question wrong , the app I had pointed you to the relevant regulation or principal , you had to get the correct answer from there , it didn't just tell you.