As my Geology teacher frequently reminds us, "If you learn the syllabus, you'll tend to get an A. They can't ask you a question in the exam that they haven't answered in the syllabus."
He likes to print the syllabus out every lesson so that we have no excuse for not having it, and we then complete past papers dating right back to 1996. This not only helps in being able to understand how to answer the questions provided, but also helps us learn to use the terms that the exam boards give you marks for.
His technique most certainly works (we get the best Geology grades in the South West here). This is most prevalent in our Geology mocks where pretty much everyone got an A (with one or two exceptions). It is also worth noting that the Geology department have the highest grades in the school.
These syllabuses, aka Exam Specifications, and past papers can be found freely on your exam boards' websites. If you want older ones ask your teacher, else they'll be floating around on the internet somewhere.
I guarantee that if you do every past paper from your own specification, plus older papers, and you do them ~2-3 times each (yes, do papers multiple times as it improves your ability to recall information), you will ace most of your exams.
Hope that helps! :-)