HELP.. How to get from a C to an A?

Make sure you Understand the key concepts, you don't necessarily need your teacher just watch a video about the topic on youtube if you don't get something.
Learn ALL the definitions and mechanisms asap and keep practising them, they're easy marks.
Past papers, past papers and more past papers.
Spend 1 hour every night on chemistry (not including homework) just to make sure you understand everything and look over the stuff you'll do next lesson so that you can use the lesson to solidify what you've learnt already instead of getting confused in the lesson (i know the feels)