Keep revising what you have learnt throughout the year and try not to fall into the trap of cramming just before the exam. There is a lot of theory in VCE Chemistry when compared to certain other science subjects (namely Physics), and in the exam, many topics covered at different times of the year are combined into singular questions, so frequent consolidation is important.
I would also advise diligently going through past exams in the lead-up to the exam period. Many students overlook completing the older papers (pre-2013) when there were two separate exams for Units 3 and 4, however they were still made by the same people, and so are very similar to what you will find on the exam! If you ask me, the order of importance of past exam papers are:
VCAA current study design (2013, 2014) *note the sample 2013 is predominantly composed of questions from past VCAA exams
VCAA past study design (most useful between 2007-2012)
External exams using the current study design (useful for practising the timed conditions)
External exams using the past study design should come last.
Make sure that you make good use of the exam reports from VCAA. Read through the comments and see what the state does badly, because those particular points are bound to pop up again! Finally, don't forget to ask lots of questions on AN, because this might just be your best Chemistry resource for the year!