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

I know my Soldiers, and I care about their well-being and that of their families.
I am fair to them, and I give them opportunities in responsibility and training that wil allow them to grow.
I give a damn, and make sure they know both when they do something that makes me proud and when I am disappointed.
I make sure that those that go above and beyond are recognized, in both awards and evaluation reports.
I counsel them, to make sure they can meet their goals, as well as mine and those of the commander.
I listen to them and get them help when they need it.
I let them know when they need to put their pants on, drink water, and do better rather than mope or feel sorry for themselves.
I am their dad at times, but I am not their friend. That may come later, when we are peers or move on to a different relationship than supervisor/ subordinate.
Never blur the lines, but don't turn those lines into walls that block communication.

Easy, you be a polite, kind and caring supervisor and not a friend.

First of all, you are not there to be their friend...you are there to be their supervisor to make sure they are doing what they need and are required to do in their capacity. You are to give them the tools necessary for success and mentor, train, and hold accountable those that work for you. You can become their friend only after they understand that you are their supervisor first. Give them direction and hold them all accountable and they and you will know where those lines are. They will respect you and if a friendship grows out of that then so be it but while you are wearing the uniform, the mission always comes first as there is someone somewhere relying on you and them to get it right every time.

On my last assignment prior to retirement, I worked for a Wing Commander who was my neighbor and good friend when we were both Captains at another station. He progressed to Colonel and me to Lt Col. We maintained a friendship but the social aspect of it changed because we knew it had to. Off duty playing golf or at dinner with the families we chose not to talk shop to separate the two. I had respect for his rank and authority as he valued my opinion as a subordinate. He also held me accountable in a situation, and rightfully so.