For initially learning the content dont be afraid to ask questions, there's a high chance everyone else in the class is wondering too - seriously ENGAGE with the lesson, if you're stuck at one point thats going to effect the rest because there's a lot of synopticity in science. Youtube videos are great too, I know Miss estruch does A level biology videos but I think she may do some for GCSE too, if not Biology with Olivia definately does and of course freesciencelessons guy is always a god send.
For revision:
Blurting - Writing as much as you can remember about a certain topic and then using your notes/textbook to cross reference and see if you're correct, the areas you are wrong write over in another colour - this should not be neat and is literally just blurting out everything you know. You can time yourself if you struggle with timing in exams too! Unjaded Jade has a nice video explaining this.
Flash cards - again, there's a lot of content so another form of active recall, just test you know all the content.
Past paper questions, many of the science specifications (especially biology) are very particular in what they want you to say, the earlier you start these, the sooner you'll pick up what the examiners want.
Ask you teacher for a specification copy so you can tick off the area you know and focus on those you dont.
Also don't leave revision until the last minute, if you want to succeed then get at it early.