Make notes on everything and really understand it. If you just learn the content you will not get an A*. You really need to understand everything you are learning, be able to explain it and just know it inside out so when they ask you questions where you apply your knowledge rather than just regurgitate facts you will do it with ease. Also practice every paper and every question you can find, even from old specifications, just for extra practice. A2 Biology is very synoptic so spend some time (not as much as the A2 content) revising the AS content. Try and group sections as well as in unit 5 you do an essay which could be something such as "explain how disease effects organisms" and you would need to use as much content and breadth as possible. Practice writing essays on all the various topics you can think of.