I would highly recommend thoroughly going through research methods if in class it will only be covered quickly.
Here is a checklist of what you should be able to do:
- define an experiment
- list IV. DV, EV, and CV for an experiment
- explain whether or not an experiment is valid
- explain whether or not conclusions can be drawn
- explain whether or not results can be generalised
- suggest improvements to an experiment
- identify and describe sampling procedures
- identify strengths and weakness of sampling procedures
- identify experimental designs
- identify strengths and weaknesses of experimental designs
- compare the role of mean and median as measures of central tendency
- compare data sets with high and low standard deviations
- distinguish between different ethical principles
- be able discuss experiments in relation to ethics
You don't need to know all of this before the end of the holidays however I'd focus on this before any other unassigned psych work. If you get extra time to spend on psych after that look at the structure of neurons (revise from year 11) and neural pathways (CNS, PNS etc.) and if you have time after that consider looking at stress
Best of luck for your preparation! If you have any questions feel free to ask.