Source source for preparing for GCSE science subjects.

I am currently year 10 and the things I'm finding helpful is:
-Physics and maths tutor (they have amazing notes and questions).
-Science Break (I think your school needs a subscription with this but it honestly BANGS, I've learnt stuff in ten minutes that I never understood in my lessons).
-BBC Bitesize (good info)
-AQA/exam board specs (make or organise your own notes using the spec to make sure you are learning the right content.
-Quizlet and GetRevising (good flashcard and note content and it's free).
-CGP Revision guides and exam practice books (keep practicing and revisiting topics to keep your memory fresh).
-Save my exams (exam questions, you have to pay for mark schemes but I just use the website for the questions, ask your teacher to mark them if you want).
-Mathsmadeeasy (more exam questions).
-Revisely and Cram (I don't really use these but I know they have some good stuff as well).

It's essential to start revising and practsing ASAP, well done for asking early! Good luck!

Don't buy anything until you know which exam board and specification you are studying with as, for instance, there's little point buying stuff for AQA exams if your school is going to enter you for Edexcel exams.