Module 1 is pretty straight forward, standard whines about needing to memorise frame sizes not withstanding. It's all about honeybee management, apiary layout, why you choose/chose the hive you did over that hive (if you assumed that the two most likely to come up are Langstroth and Nationals perhaps).
For your chosen method(s) of swarm control and prevention, why do you undertake the steps that you do, what does it achieve and why?
Understand the basics of Honeybee lifecycle, how long from Egg to emerging for Queens, workers and Drones. Why do queens go drone laying, what causes drone laying workers and what actions can you take to rectify that situation? If you lose a queen what can you do? Why do you clip (or not as the case may be) and why do you mark queens? What do you put on your record cards? Why do you keep record cards?
I posted on here somewhere the paper for Module 1 for 2010, that should give you a reasonable idea of the sort of questions that come up. All of them list the points that you'll get for the answer so if it's a single point, give a single sentence answer, 10 points give an answer with around 10 different things and so on.
Section C on all the Modules is now far more about demonstrating that you understand why something is happening or why you do something to rectify a situation. Sections A, especially, and B still have a fairly heavy emphasis on remembering stuff. This is apparently changing in future to be far more "demonstrate an understanding of..." but I believe for the march exams at least, the current format will remain.
Contrary to popular belief, on here at least, the modules aren't about reciting the approved BBKA "Thou shalt keep bees thusly" but if you're going to claim that Jam is a brilliant anti varroa treatment be able to back that assertion up.
Module 3 is far more involved. It is supposed to be shifting emphasis from Disease to honeybee health it's a subtle distinction, but in addition to covering diseases I'd also think about things that you do to keep a colony healthy and why you do those things (outside of an IPM scheme, changing combs perhaps)
There is an expectation that you'll know the Latin/Scientific name for things, at least for the main conditions. There is a big emphasis, unsurprisingly on the Foul Broods and Varroa but you also need to what's a virus, what's bacterial, what's a parasite and whats a fungal disease and what else they might indicate is going on in your colony. Apiary Hygiene might appear in module three or it might appear in module one, IPM is certainly likely to come up.
Read up on things that you don't use, understand what they do and perhaps why you don't use them. In an ideal world I wouldn't go near them with a ten foot barge pole, but I included Pyrethoids in my IPM scheme in the Module 3 exam. Outlined why I don't use them as a matter of course and why I might consider using them (and what actions I'd take if I did use them in an apiary).
The FERA booklets for AFB/EFB, Varrao, Small Hive Beetle and Tropilaelaps are no brainers to use to study for module three, they're free, excellent and cover about 75% of what is likely to come up.
Things that aren't that common where you treat for varroa like Acarine and Braula coeca are also worth reading up on.
To a lesser degree Wax Moth, Woodpeckers, mice etc are all likely to make an appearance but probably not in the big point questions unless part of a wider preparation type question. It's not essential but knowing that a mouse is (I hope or I've forgotten already)
micus domesticus won't hurt but you wouldn't fail it if that's all you forget
[edit]
I'd also add that I found both these modules incredibly useful, especially as we had study groups for them within our association. Even if you don't intend to sit the exams I'd recommend doing the study groups. I think it's very easy to "tunnel vision" in beekeeping, you do something
like this and forget to question why you're doing it and whether it might still be the "best" way of doing something; these Modules force you to take a step back, dig down into why you do things, what else is going on out there and make you consider alternatives.
[edit edit] Link to module 1 paper:
http://www.beekeepingforum.co.uk/showthread.php?p=60229#post60229
I thought I'd scanned the module three paper but I haven't which means it's buried somewhere I'll try and dig that out and get a post up.