What's on the syllabus? At Cambridge, it's the following:
Not overly helpful, eh?
Anyway, if yours is similar, I'd say you should learn the following:
Property offences - people don't seem to like these, but they're not too difficult to get to grips with since they all build on theft (bar handling stolen goods, which I never really learned in detail). I'd definitely learn these in case you get a nasty non-fatals/homicide question you'd rather not do. Fraud is also very important, so make sure you learn this!
Non-fatals - learn these well. They're fairly easy to commit to memory because they all build on each other and, occasionally, there's some overlap (e.g. mens rea for s.47 is the same as common assault (
Savage), actus reus of s.18 is the same as s.20 GBH (naturally, since s.18 is "GBH with intent"
)).
Other, more weird non-fatals - I never learned things like "administering a noxious thing"; I knew of the offences, but I didn't know any cases. Thankfully I didn't have to use them - assault-s.18 are by far the most common non-fatals in problems.
Homicide - learn murder and voluntary manslaughter (diminished responsibility and "loss of control") well. I'm pretty sure you won't need suicide pact unless you've seen it come up in the past, and even then it's so small that you could probably get by just using the statute (even without cases). Also learn gross negligence manslaughter, but don't worry about corporate manslaughter or so-called "subjective recklessness manslaughter".
Sex offences - learn these and familiarise yourself with the SOA 2003, since the presumptions (s.74?) are a pain to try and apply in the exam if you don't know in advance roughly what they say.
Secondary liability - learn joint enterprise; it comes up a fair amount in problems (particularly in relation to murder) and is fairly simple to understand and apply once you've committed it to memory. Also learn the stuff on aiding, abetting, counselling and procuring
Inchoate offences - I don't remember much of this, but learn it. Also, if you've got access to a copy of
Padfield on Criminal Law, there's a useful table on page 36 (?) which summarises inchoate-ception pretty well (e.g. whether it's legally possible to attempt to conspire).
Defences - leaving aside the special and partials (which relate only to murder), you'll need to know duress, insanity, automatism, self-defence, intoxication and self-defence. Bear in mind too that you'll need to know the effect of intoxicated mistakes (I can't remember much about this, but Herring's textbook covers it pretty well).
Policy questions - if your paper's anything like ours, you'll be expected to set criminal law in context. Think about the kinds of issues that the criminal law does/doesn't deal with, and whether it should/shouldn't.
Brown, for instance, is fairly unlikely to be the basis of an essay question, but think about key cases and whether you agree with the outcomes - and also how to draw different areas of criminal law together. I was asked a question on, I think, domestic violence law - naturally I mentioned the Domestic Violence, Crime and Victims Act 2004, but I also drew on my A Level knowledge of the old law on provocation and considered whether the reform of the provocation defence (now "loss of control") made it satisfactory for female victims of domestic violence. It seemed to go down pretty well - I'm just lucky I had that old knowledge to draw on!
Books - I can recommend
Herring (text, cases and materials), although I've heard good things about
Simester and Sullivan and
Ashworth. I'd steer clear of Nutshells and the like - it's tempting to use them, but they're so superficial that you're more likely to confuse yourself.
Anyway, sorry for the long post - hope this helps, and best of luck with your exam. Bear in mind that this is Cambridge-specific advice, so don't be alarmed if your Criminal paper doesn't cover all of these areas!