How do you draw the line between being a good supervisor and being too friendly?

You start out making sure they know the difference between business and friendship

A good leader is a subject matter expert. They teach everyday. They display pride, professionalism and dedication. They are caring and cordial & they make it clear they expect others to rise to that level. People respect that and will like them naturally. At least that's my experience. I had great mentors.

SrA Kampe, being a first time Supervisor is rough. ALS, doesn't really address this issue that much. When you go from being one of the "boys", to the boss. I would just privately talk with each person and let them know where the "line" is during duty hours and off duty. If someone is not able to maintain the standard you have set; then you can choose to either give a verbal counseling session, and a MFR for the reason, or a formal written counseling session. Most times talking to the individuals and letting them know about what you expect and what your standards are will correct the problem. If not, I've given you the advice on what to do as a next step.

Maybe it's because I was almost 28 when I enlisted, but I've never had an issue being friendly but not their friend. As some have said above, if you find yourself unable to carry out your supervisory duties then you need to cut ties and reevaluate your relationship.

Saw this the other day. Pretty spot on.

The answer to your question is in the question, you draw the line. You make sure the troop(s) clearly understands you are there to help anyway possible but you are not there friend. Don't put yourself in situations where they can misinterpret your actions as an invatation for a friendly relationship.