If you already have a comprehensive summary with everything you need for the test, you can just take this document and break it down into smaller pieces. (as discussed here) In case you don’t have an overview of the whole topic, just start to type in questions and answers, even if you are not sure, how important these facts are. You can’t lose doing this, as you can always change the content, delete the cards, or restructure the cards differently in the card sorter (explanation follows below). For one question ideally 3 facts have to be remembered. Try not to exceed 8.