Mathematics & Further Mathematics - practice, practice, practice! literally the most basic yet most valuable advice one can receive for a methodical subject like maths. do every single practice question/ exercise/ past paper question possible and make sure to mark your work against the markscheme, ensuring that you haven't omitted any steps or workings which could potentially lead to losing marks. you'll find that the questions begin to get repetitive after a while; once you master the method, you'll be fine - no matter how the question is asked or framed.
EPQ - too often, students get lost in aiming to produce the best possible essay or project or whatever it is, losing sight of the fact that a lot of marks are actually given out for commitment & organisation. keep a journal. update it weekly of the research or work you've done towards your project. your assessor wants to see that you've been regularly working on your EPQ and that you're committed to it; by keeping a weekly log, it proves that you didn't just panic write your EPQ in the 72 hours leading up to the deadline.