Successful revision tests your understanding of content. So try recording your answer to a test question and critically listen back.  Is your explanation clear and precise?  Look at a test question and write an essay plan to show how you would answer the question.  If you are a visual learner draw a mind map to show how you would tackle the question.  Mind maps can help you see correlations and identify missing bits of the jigsaw.  All of these methods will help you identify gaps in your knowledge and show you where you need to concentrate most.