It's the old chicken and egg problem-how do I show prospective employers I have management experience when I have never been a manager?
Many leadership and management courses are available at Cornell and are open to graduate students and postdoctoral scholars (postdoc associates can take up to 4 credits per semester: how to register). Some of them are listed here and the most relevant ones are highlighted. Remember, with your advisor's and the instructor's permission, you might also be able to audit a course.
A popular course that BESTies have taken is ALS 5100, Leadership Development.
Consider reading the book First Break All the Rules, by Marcus Buckingham and Curt Coffman.
It's not too early to think about how you describe yourself in terms of accomplishments, problems you have solved, or the value you add to the projects in which you are involved. Believe it or not, employers will take it as a given that Cornell PhDs and postdocs have achieved a level of excellence academically, have published and have given invited scientific talks. What they are more interested in are specific skills and competencies that you have acquired during your training. The Cornell Career Services Office offers an excellent summary of these transferrable skills and strategies on how to approach self-assessment. Here'a quick chart you can print and use to check off your own skills and how much you enjoy using them.
Examples: organize a symposium
- PMF.gov (Presidential Management Fellows Program in personnel management)