Use the candidate workbook - it is an excellent study tool, often neglected.
Read the introduction and how to use the manual - one section at a time, read the objective, answer the questions, review the answers. The answers keys not only tell you the correct answer, they often tell you why the answer is correct, and why the wrong answers are wrong.
Repeat the questions until you understand the process, but more importantly, as Quero has said, use this to learn the underlying principles. They are not rocket science, and things we can often apply to every day life. Gas volume in a balloon gets bigger as pressure decreases = the BCD, of course, temperature increases have a corresponding increase in tank pressure, sea water weighs more than fresh water because it's full of - well - salt, amongst other things (including fish poo).
Don't get lost in the numbers - the concepts are quite simple and once you understand them it will make applying the numbers easier. The questions can be learned by rote, but consider that as a DM you would be expected to understand and explain these concepts, whether you are working or not.
Study groups work well - if you have some peers then this is of great help. Helping somebody else to understand something increases your own understanding immensely. I learned more from teaching than I ever did from being taught.
Hope that helps - and good luck,
Crowley
