Notes are key for history. Notes that you know, and can revise easily the days before the exam. Do you have any notes?
If it's just a massive book that you have, and you don't reckon it'll be feasible to read it all, maybe go through a couple of past papers, and for each question make a list of bullet points to answer them?
My advice would be though to preferably have notes that cover everything, read that till it's stuck in your head and then you should be able to cover what comes up in the exam. If it's doable through a book then do that, maybe underline the key points so you can skim next time. Combine that with a knowledge of the exam paper question styles and how to answer (e.g. 8 points for an 8 marker) you should be good.
As to revising itself, I like to recommend turning off all phones, laptops etc, taking the battery out and whatnot. For something like history there's a lot of reading, so I like to sit near a window, read for say 10-15 minutes, then stop and look out the window at the street for a bit to clear head, and then continue. Not getting distracted by the net is key, but having a short break to clear the head helps too.