If you have read and understood the text you are studying, you will be able to identify key scenes/chapters with that character present. Once you have identified those key scenes, which should be made clear by your teacher or tutor, you should set about learning at least three key quotations from those scenes/chapters.
Next, you should mind-map those quotations, one by one, and list all the literary techniques they use and what effect they have on the reader. Following this, you should use a different coloured pen to link that quotation to another part of the text. Knowing these links will allow you to score even more on your GCSE paper. Once you have your sheets of paper on each quotation, you can use these for revision, to create flash-cards, and of course in your practise essays.
While you are doing all of this close analysis, you will be learning loads more about your studied text too. So there you have it: a really easy way to expand your learning of key characters for GCSE!