Flashcards are a great way to break up a practice session. Put the instrument down and learn an important part of note reading - learning the notes! I have found that I can start flashcards from the first lesson, long before students actually start note reading. This gives them the foundation for knowing their fingerboard geography. After experimenting with various kinds of flashcards, these are my absolute favorite for strings. The back has the finger placement as well as the note name.
In my studio everyone passes off their flashcards every year in January. See my blog