I've just finished YR11 and the whole exams business so I'll try to give some at least vaguely useful advice.
My targets were all A's, A*s, 8s and 9s too, so I guess we're sort of on the same wavelength when it comes to that. I was also the 'smart' girl - always doing well in tests, topping the class etc.
I will say though, no matter how much revision you do, unexpected circumstances may arise during the exams that are completely unavoidable which may ruin your revision plans etc.. for example, I was going through some family issues as a young carer, which had to be dealt with and left me feeling quite down and not in a revision mood. It took me quite a while to do notes and we weren't taught a lot of the content so I felt a lot of the pressure which is quite dwelling on your mood. All in all, during the exams themselves I felt pretty comfortable (except some science - covered below) and this was probably due to working so hard before starting official revision, so hopefully that paid off. Also, I relied upon a lot of what you could say is like common sense, natural knowledge as a higher level student.
It's important to note, different ways of starting revising work for different people.
For me, personally, before starting the actual process of learning the content, I wrote revision notes on EVERYTHING to ensure that if worst comes to worst, the night before the exam I had some information to look over and almost rely on. My focus wasn't so heavy on learning the stiff purely because throughout my school life I'd worked so hard, always keeping up with homework and doing extra research to make sure I understood everything etc. (I think it's appropriate to note here that if you're in lessons and don't FULLY and CONFIDENTLY understand a topic you MUST go and ask as soon as possible because when doing your revision you don't want to be at a halt (especially during half terms) just because you don't understand anything, as it's quite pressurising to have to learn something by yourself, which you previously didn't understand with a teacher). These revision notes which you make will be your rock throughout exam season. It was important for me to make these neat and pretty - otherwise I wouldn't have had the will power to revise at all. It's important to start these early. I started mine February half term and didn't finish them on time. This may have been due to my school being pretty terrible and actually never teaching us the paper 3 content for the sciences so I had to teach it myself on top of doing notes. (I think its appropriate to note here that the sciences have a lot of content so its important to learn paper 1 and 2 content early and know it off by heart so that you can focus on other papers which you'll be less confident on - theoretically then you'll only need to recap a few nights before).
Hence, if I was giving a rough guide I'd say its best to start over Christmas. Get yourself organised. A notepad per subject. and start noting yaayyyy. Do maybe an hour a night to begin with. If you found yourself bored over summer you could start (never too early) and this would mean you wouldn't have to do as much per night.
if you want more specific advice, maybe on some certain subjects (we would do the same/similar English&Maths) then just ask