I'm retaking BIOL1 this year as I got a B in it last year and wanna bump up my UMS this year to secure an A, in the case that I don't get an A* at A2.
My advice would be to initially learn the topics one by one; after this only memorise in detail (understanding them properly would be good too, as you may have to relate particular information to other questions, but if you find them too hard then just memorise them) the 5 mark question topics (lungs, heart, immune system, microscopy etc) as these ones hold two 5 mark questions every year and if you can memorise them off by heart then they're an easy 10 marks. I wouldnt spend hours and hours memorising in detail other smaller topics just do past papers, tons of them. After a while you pick up what you need to know for organelles, enzymes and other smaller topics and you'll be getting the 2-3 mark questions correct everytime.
I cannot stress how important past papers are, mixed with flash card methods (diagrams for cells and structure of the heart) as these helped me so much to understand the exam technique and get little bits of important information memorised. Best of luck everyone, Jack.