I agree with you that chemistry is arguably one of the hardest A-levels out there. It's tough, but it can be done !
I'll tell you how I revise (not just for chemistry):
I make hand-written notes throughout the year, and also make questions based on these notes, saving the questions on my USB. I then answer the questions immediately or later sometime and save the answers in a separate folder so I can refer back to them. I find this method of revising personally more useful than simply re-writing the notes! Some people also like to use flash cards and stuff, but it is really up to you to find what works best for you personally!
However, the most important source of revision that you can do I think is past papers - practicing by doing past papers helps to identify areas you are weak on; last year at As, I was getting around B/A grades when I started past papers for chemistry, but by identifying my weak areas and revising those specific areas, I was able to boost my marks and I ended up with a bang-tidy A at the end of the year !
With great difficulty. Currently I complete many, many past papers and give them to my teachers to mark. I then go over the mark scheme myself and see where I have gone wrong, look back over my notes, make posters and attempt the wrong questions over and over again until I get them right. I recommend this a lot as it has helped me so much with my revision. If you ever need any help, message me!