what id do is get sample/past papers and read through 5/6 of them. write out all the topics in them. go through that list and assess what you already know and what you have to study. do a quick revision of what you know to keep it fresh on your mind, and study the rest. you will save so much time because you will not be doing anything unnesccesary. if you are still struggling try to link topics, for example whatever you are studying should tie in nicely to the next thing that happens after, and it will just flow into the next topic, again cutting down on your workflow by combining them. Good luck!
look at past exam questions ... for example russia is a guaranteed question.Look at what comes up frequently alot of the time you will get questions coming up in diffirent ways but they mean the same thing .....plus you can leave out 1/3 courses if you like, history students have alot less stress this year!