Hi, I want Medicine too and I am doing Chemistry. If you do all the exam papers (including mocks) and dont have to refer back to the book then you know the chapter really well. Thats how I learn and its worked so far. Also do practise questions from the book that contain maths parts in experiments. Good Luck!
I just did the LC and got 99% in chemistry and I would say the best thing to do is to focus on the main topics. Thats not to say that you should leave the rest out, but there is a huge choice in the LC exam and the core topics such as Organic Chemistry, Atomic theory and Volumetric Analysis frequently carry alot of marks so knowing those inside out would give you a huge advantage.