I just came across this article about practice habits and I plan on sharing it with my students:
I found it really interesting that longer practice time and more repititions did not show huge improvements. Practice needs to be done carefully and students need to know that they must NOT practice their mistakes over and over. This is one reason why I don't do grading based practice time or practice cards. We really should be focusing on the results of practice and this can be done by giving practice assignments that require a specific accomplishment.
I just made this little poster for my classroom to help remind students about the need to practice carefully and slowly: