It's not for everyone but I mostly learnt by error. Before I even began any form of revision I'd look up old exam papers - the oldest you can find that have the same criteria and attempt 3/4 of them, even some from different exam boards. Find where the holes in your knowledge are and fill them. You'll start to notice that a lot of questions are repeated but rephrased, if you look at the newly added modules that occur each year they always have very specific questions relating to them. Write model answers, memorise generic formulas and processes, read the chapter from your revision book and repeat a few more past papers and repeat every time you find a fault until there aren't any
This is more of a strategy to ace an exam than become proficient in a subject. But it's a great way to speed learn how to pass a specific criteria exam. I applied the same thing to all my A-levels, I did maths, further, Chem, bio, physics. Worked especially well for Chem and bio.
The only exemption is the maths and calculations. Those I mostly just spent an hour or so hammering out a few questions, matching the step to the mark scheme and memorising any necessary equations and formula. That way even if you botch a rounding error or use the wrong valued you'll get the majority of the marks based on theory.
*I sat WJEC in 2014*