I too did those courses and the best advice I can give is to stay on top of the workload and revision (start early) but also just enjoy your time at sixth form or college (wherever you are doing them). Its a great few years where you can study the courses you have opted to do. Some advice regarding the maths, do plenty of practice alongside lessons. For me it was easier to revise as it was more involved than just reading notes as is the case with the other two. With subjects like these, doing an EPQ probably won't make much difference so if you need to drop it so you have time for your main subjects, don't worry.
Hope that helps.