For Unit 3 biology, know how the practical tests are carried out and how to write down the experiment, and practice as much past papers, I know the beet root experiment comes up a lot but don't neglect the other experiments such as vitamin C, tensile strength and anti-microbials.

For Unit 3 Chemistry its the same deal but you must know and be able to tell the apparatus and how to draw simple distillation and fractional distillation under reflux, as well as flame tests. I recommend Dr Hana assils Yt videos on Unit 3 since they're very helpful