I had a friend last year who was predicted a load of 7s/8s and a few either side as a maximum but he worked extremely hard (very very very) over summer term/ HT and the exam period to come out with 9 9s and an 8.
I got 12 9s so if I give any advice, I'd say to make sure you know the content top to bottom and inside out for every subject, with really focussed revision on the 3 days before exam day, doing at least a full set of past papers for each subject in this period and self-marking and reviewing. Also make sure to do loads of past papers/questions in general (even other exam boards if you run out) constantly learning from what you get wrong and fixing gaps in knowledge. For English, just keep writing and reading and waffling - that does help, but don't repeat stuff you've already said. Make sure you do stuff under timed conditions. For maths, do questions, don't look at mark schemes until you have an answer, and make sure the problem solving techniques are ingrained properly.
For history, just know the subject and be genuinely interested. In fairness, that applies to all subjects to help drive up grades.
BEWARE of saying 'should have gotten xyz' - this generates complacency. Which is bad.
Also don't trust the advance info given by exam boards but that might not exist any more.
Hope that helps!