Dw I started revision 2 days before my first exam and got mostly A*s, you just have to be methodical. First of all, don't look at your phone from when you wake up til about 8pm. Don't turn on your computer/tablet either, that counts. No games. Nothing. Break up your time into slots of a few hours each and then do the following:
Read each topic (just stick to cgp revision guides or something) until you understand it (don't take any notes it takes too much time and is inefficient) then answer questions/write an essay immediately after the end of the topic (perhaps from past papers or text book) to solidify each one, then move onto the next topic. And by topic I mean big topic, will be equivalent to maybe a chapter in a cgp guide. When you're done, do some past papers. The night before an exam, do a couple of hours of last papers, when you're in pre-exam mode you'll find it very hard to take in new information by reading it, past papers are the best. First thing you need to do is timetavle your revision, you should be able to manage one slot 9-12, one slot 1:30-4:30 then idk when you have dinner but you can easily get another 3-4 hours in there every day.
If you want specific subject advice just ask.