Firstly, you must have read the text through at least once. From here it can be helpful to create mind maps of quotations that match specific and relevant themes so that in your head they are organised into categories later when you are faced with a question. Choose quotations which are short and easy to memorise and most importantly, that you understand. It can be conducive to more original work to pick some quotations that you may not have done in class especially if you find them personally interesting. From these mind maps perhaps add some analysis to each quotation as a useful revision technique so that you can relate them quickly and effectively to the theme in an essay later.