Teach to learn
One of the most successful ways to learn something well is to teach it. Select a topic that you feel you know well and try teaching it to an imaginary person. As your teaching proceeds, you will quickly realise where there are gaps in your knowledge and understanding. Immediately you will begin to identify clearly what it is you are explaining. You will become aware of any aspects that you are less clear about, and can focus on those. Imagine you are explaining something to someone who keenly and urgently wants to understand. It feels like a much more positive and purposeful activity. Sometimes you can even do this to an interested partner, friend or fellow student. Try preparing a topic with which you do not feel familiar, in order to explain it clearly to someone who wants to know about it. You may find this simple method works well for you.