Revise GCSE maths (any good GCSE book should cover these fundamentals) focusing on rearranging equations, scientific notation, ratios, significant figures and interpreting data. 

Using any good GCSE chemistry book review; GCSE analytical techniques and various ions tests, common reactions eg: neutralisation, oxidation and reduction, how to calculate relative atomic masses, ionic and covalent bonding.  This information is available on GCSE bitesize and kerboodle or Chemistry for you books.