oh, i went through the same thing last year for AS. Basically, you can't sit down and read a book and expect to concentrate, i found that out the hard way. So what i did was not try and learn stuff off by heart, but i just read through some notes, after a good night's sleep, it helps in concentrating, a lot. Then i just went through past papers, and i looked at the mark schemes, since i didnt have time to actually do them, and they were subjects were learning was essential, not much calculation or logic...and basically the day before the exam and the morning of the exam itself i just kept looking through the past papers and the markschemes, after re-reading the notes, and just ignoring the book's existence. I do remember i felt like i became one million times better after looking at the pat papers, things just started to make sense and i actually knew wit im supposed to do..
hope this helps, and good luck!