Start reading research papers from different journals, would be a great place to start! Try and read a variety of different fields: neuroscience, cognitive, social, abnormal, and then different sorts of research like brain imaging studies, neuro-psychopathology, animal studies, maybe qualitative analysis if your course covers it. It'd be a good idea to stick to ones that relate to your modules because having extra independent reading is always a great thing!
I think a good skill we learnt in the first semester was summarising research articles. That'll be very handy for essays. It took me a while to getting to grips with reading through an article and picking out what's worth while noting, it took me ages to read trough an article at first. So I'd suggest pick an article, read it and summarise it. Briefly explain the article, highlighting important bits, and then evaluate it.
Now for evaluating articles you need a good idea of what makes good science, and so need some knowlge on research methods. So I'd suggest reading a text book on psychological research methods
And one book we read in our first year which just opens your mind about good science is 'Bad Science' by Ben Goldacre. It's not at all text book, more of an easy read. But I find it interesting
One other thing which I suppose you could get your head around is statistics. But I wouldn't say that's really necessary, it'll be hard for you to work out what you need to know for your first semester and so you might end up over complicating it but looking at stuff that's too advanced. So I wouldn't worry about that.
Just some advice
of course I didn't do any of this but looking back it would have been beneficial.
Good luck! And I hope you fall in love with it as much as I did