For materials, the most important one is the study design document off the VCAA website. You need to be familiar with everything it says about the PSM, the glossary and every key knowledge and every key skill dot point it lists for IT Applications. All that is examinable material. I found it really helpful to write out a set of notes using each dot point there as a basis (e.g. write out absolutely everything I knew about that particular dot point, and then go research it more to add onto it etc.).
You absolutely cannot give one topic any more preference than another, all of them have an equal chance of appearing on the exam and hence you should work towards knowing everything on the course like the back of your hand.
In order to not reiterate myself, I've listed a few resources which I know of here:
List of IT Applications Exam Revision Resources Be sure to have a look at the stickied threads and the resources that Huss48 has uploaded too.
Practice exams are handy for practicing your exam technique. The quality of the practice exams aren't that good, so don't put too much weight on the exams produced by companies. On the other hand, focus quite heavily on the VCAA exams (2007 onwards are a
must really, you could go earlier if you want... but it's not really necessary and you'll find more questions than not which are slightly too irrelevant to the current course).
SACs - ranking matters more. Exam matters more so. Don't waste your time thinking about rubbish like "what's possible" though, you should be 100% focused on working towards killing the exam.