Hey Spi,
The things in preliminary that you need to understand are examples of the 7 information processes in an information system & the information system in context diagram. You also need to be able to apply these to scenarios too.
Social & Ethical issues are always asked & are easy marks.
If you're doing the option topic 'Multimedia Systems' then you may want to revise 'Roles of people involved in systems development'
Understand the context & DFD diagrams as you may be asked to draw one.
Know the difference between participants & users. I think this is the thing that a lot of people stuff up with in exams.
Good luck!