I took the same three subjects- what board are you doing? And are you doing lit or lang?
For psychology I would just advise you to learn the essays. Obviously read around the topics and get a good understanding of them, but then make a good essay for each potential subject that could come up in the exam, check them with the mark schemes and maybe adjust them to make sure they're top quality, and then learn them.
I did a pretty uncommon history exam (at least I looked but couldn't find anyone else on here who did the same paper), but I would say for any history paper you really need to a) have a strong essay writing layout in your head, with a clear introduction, body and conclusion that you can alter depending on the question, and b) have a very good knowledge of your time period, as they sometimes throw out some nasty questions that you have to really think about to answer everything. In my exam, at least, I found it better to have a wider breadth of knowledge concerning my time period- with some details- than completely focusing in on the one area that I really like (which I ended up not even writing about in the exam).
I'm just going to give you advice for Lit here because I don't know if you're doing it, but it's what I did: don't just read the assigned texts. Read as much about them as you can. If you're being advised to read them or if they're any good for the course then you'll find plenty of critical readings of the text, often by other famous writers and critics, out there. Learn as many different interpretations of the characters and their actions as possible, find out a bit about the author and what prompted them to write, and make connections between the texts, both in terms of their themes and the way they use language and structure.