The Pareto Principle, often called the 80/20 rule, is the broad observation that approximately 80% of outcomes or results come from about 20% of your inputs or effort. Therefore you should concentrate on areas where you can get 'big wins' with comparatively little effort.
We can apply this idea to university study by focusing on 'high-yield' topics (the stuff that gets us the big marks) and by using active learning techniques that can offer better results with less time invested.