Many statistics departments in institutions throughout the world hire graduate students to teach and assist with the teaching of undergraduate and graduate-level statistics courses. As many of these graduate student instructors and graduate teaching assistants (GTAs) have little or no previous experience teaching statistics, statistics departments are faced with the challenge of preparing their graduate students for teaching roles. Articles have been written sharing various departments' strategies for GTA training and development programs, however, articles are often not supported by empirical research. This article provides a review of empirical research regarding graduate students' preparation for teaching--first focusing on graduate students in statistics, specifically, and second offering what can be learned from studies of graduate students in other disciplines. We conclude with ten research-based recommendations for preparing graduate students to teach statistics, along with practical ideas for how to implement them.