It can be very useful to look at old exam papers (OU Law Students can access these through 'Elite') - but even more useful to take a look at examiners reports. These often highlight common mistakes that have arisen. If you read a few reports you'll see that the same issues frequently turn up.
One comment I'd like to stress appeared one year (though it is a perennial) - "Some students in fact forgot to apply the law to the facts at all, and simply listed cases; although these were usually relevant ... it was very important...to apply the rules and principles as well as setting them out."
Cases are important - especially in English Law where precedent plays a key role - but there can be a tendency to fixate on memorising case names and facts. I've known students who have sought to memorise over a hundred cases. (to which I say, how many cases can you discuss in a three hour exam in which up to an hour can profitably be spent choosing the best questions to answer; planning the answers; writing them; and reviewing them?)
Use cases to illustrate a point you are making; to support your argument; to demonstrate different approaches to the issue - but never just recite cases and their facts.
How should you "revise" cases?
The first task is to select the cases that you plan to revise. As you revise each topic, think about which cases are most important. Clues can also be found elsewhere - what has the manual; textbook; tutor stressed most? (My students will be familiar with me banging on about ...)
[W201] Entick v Carrington; Ghaidan v Godin-Mendoza; Campbell v MGN; Carltona v Commissioner of Works; Associated Provincial Picture Houses Ltd v Wednesbury; The GCHQ case (Council of Civil Service Unions v Minister for the Civil Service); Porter v Magill; R v Ghosh; R v R (Marital Rape); R v Cunningham; R v G (Recklessness)...
Prepare brief notes. Students, almost since "time immemorial", have used revision cards to prepare for exams. The value of these cards are that they require you to condense the information. This is a (the?) key process in revision - (there are some professionally written cards on sale - some value, but you lose the process of condensing yourself - similarly, copying out from a text or revision book has the same value-deficit). There is some value in reviewing the finished cards frequently.
Consider the application of cases. Cases should not be used as decoration. They are a vital part of legal argument. Consider where and how you would deploy these cases. This is where using old exam papers can come in useful.