Make sure you understand what you're being taught as soon as possible. If you don't understand at first, try and figure it out that day or the first weekend. If you can't, ask a friend or a teacher to explain it to you in a different way. Don't think you can leave it until study leave to sort it out, it's not a good way of working and you'll be unlikely to be ready for the exam with all of your other subject commitments.
When you begin to revise, try to make sure you remember everything (by doing a selection of questions from a book, depending on how much time you have) before you start past papers, so you don't waste a paper by not remembering how to answer an easy-ish question. It's fine if you get stuck because it's hard, but you should at least know the route you need to take even if you can't complete it. Spend a little more time revising A2 modules as opposed to AS modules as the A* is based on you getting 270UMS from 3 A2 modules, as well as getting 480UMS in all 6 modules.
When you start past papers, make sure you have no distractions, and do them in the allotted time limit. Again, don't worry if you can't finish it in time at first, because you'll get faster as you become more familiar with the style of question, and at least you know you've got to do something about it from the start and not closer to the exam if you start timing yourself too late.
Once completing a past paper, make sure you study the mark scheme and learn the examiner's method. You will get a better understanding of what you get marks for, so you know how to maximise method marks if you can't finish a solution.
Something that I found very useful is also reading the relevant Examiner's report. I found that not many people do this, but it's a gold-mine of information. You can find out what questions most candidates found hard, and the examiner also gives tips as to what sections of a module that candidates should concentrate on. I found it really useful.
Finally, when it comes to exams, don't panic if you found a paper hard. Chances are, most other people did too. Also, you have 5 other papers to concentrate on, where you can grab back any marks that you may have lost on your way to an A*.
Good luck!