Everyone have their own difficult subjects. For example, if you are bad at maths I would recommend you to do Stiochiometry as much as you can. In my opinion Chemical Bonding is the most important chapter. And I would advise you to learn by heart as many experiments as you can, becouse experiments usually take about 60% of a test.
I got a H2 in the mocks, and hopefully am aiming for a h1 in the actual thing, if you send me your email or something I can tell you which chapters are best to do, personally I think doing them by question is the best method (e.g. learning volumetic analysis ensures you will get 100 percent in q1 of the paper provided you do it correctly)