Dismantle the learning material into the smallest, still meaningful learning units and formulate the questions and answers as simply and as clearly as possible.
Make sure you write everything down correctly, so you do not learn any spelling mistakes.
When learning in the group or in the class, it is useful to categorize the cards separately according to subjects or learning areas. See also Creating a Folder Structure for Flashcards.
Be critical - think carefully about what you want to keep in your head! You should only write down the course material you are sure you want to keep in mind in a year.