I suggest you should venture off the beaten track of the typical introductory legal system books. They give you an overview of how the system works, but you might want to look at something different too. I have to say that apart from a two week introductory course (or a small module that some other unis do), the rest of your law degree isn't much like reading Williams' Learning the Law or any other similar books. Sure, they're imortant, but you may want to try an introductory book on a specific topic, say, constitutional law, contract law, jurisprudence, criminal law etc. It depends on how ambitious you are and how much time/money you have, but doing this would give you a much better idea of what most of your three years studying law will actually be like.