Recommended Reading
It may be stating the obvious, but to improve your mathematical competence and confidence you need practice. And lots of it!
Invest in a revision/ practice book that includes exam style questions, such as the GCSE Mathematics Complete Revision and Practice books from CGP Books.
And make use of mathematics resources available on the internet, such as http://gcsemathstutor.com, where you can download free worksheets (with answers) and exam papers.
