Going into Year 11, and got a mark significantly more than the grade 9 threshold in our Year 10 summer mocks - personally, to do well in Maths, you have to work - and work hard. In my school, we are doing three year GCSEs and we have basically finished the Maths specification in well under two years - in no other subject are we even close to finishing.
Strive to get full marks in everything - homework, classwork, mock exams et cetera; when you don't, find out why and ensure that you know exactly what went wrong and be sure to correct it.
And, finally, when revising, do not waste valuable time on things you are confident about - however, do not forget to skim these elements to ensure that you have not forget very small, yet important details.
Good luck.