I want to apply to oxford university to do maths , how do i increase my chances? and are these gcse grades ok?

First of all these grades are fanfastic!! Well done! Secondly, you should go on Oxford uni website and look under the tab 'entry requirements ' you could also call them up, another thing u could do is type 'university league tables for 2011' and click on the guardian news online link, you can also type in 'university league tables for mathematics 2011' in google and you should get the best universities for maths, as for extra curricular activities you can become a volunteer at an accountancy firm or tutor in maths, good luck :)