would recommend using sites like bbc bitesize and seneca, if that's your thing.
primarily though, cgp revision guides are the best and some come in a bundle, where you can get exam questions to practice as well.
on yt, you have freesciencelessons, primrose kitten (who is a little inaccurate), and I'm sure you can find many channels by searching.
if your school has it, hegartymaths is great, although he is a bit slow in his videos. they are useful though.
for maths, i'd recommend using corbettmaths just to keep your mind up to speed and fresh. their 5 a day is great and will help you realise where to revise.
my best advice for revision is to look at the spec and kinda make a checklist out of it. revise everything that is on there and be sure to do past papers.
when i was revising for my compsci gcse, I literally did every past paper available and I found that the questions are repeated every year, but changed up slightly. this basically meant my mocks were awesome and i got a 9 as my grade
hope this post helps