Hi, I got a grade 9 in GCSE History last year. I would suggest making mindmaps of each key topic, for example, the Berlin wall and then outlining the causes, consequences, and events. For dates, I would use flashcards and then make sure you have a good structure for each of the questions (I don't know what exam board you are but your teacher should be able to suggest a structure for you). Once you feel you have learned most of the content you should do as many practice questions as you possibly can, even creating them as you go along (i.e once you've covered the Berlin wall create as many questions about this as you can).