I used the specification on the exam boards website as a 'tick list'. I used the textbook and made bullet points summarising all the relevant information but making sure I included all relevant points that I could be tested on, drew diagrams, highlighted key words and made it look visually appealing (but only if I had time).
Then, I read through it (and made sure I understood it!) and then didsome practise questions from a book to test my understanding. Once I had finished writing notes for one topic, I would do a past paper (in your case, it would probably be best to look at sample assessment materials on your exam boards website).
If I had time, I would make flashcards of key words and their definitions. However, for English and Maths the best thing to do is practise! Do loads of questions and papers
Hope this helps
I managed to do really well in my GCSEs using this technique but it just depends on how you learn best. Some people I knew did mindmaps summarising each topic.
Good luck for those exams!