My DCs had an almost perfect acting HT last year.
They MUST LIKE children. (And never look at them as if they are something the cat has dragged in. It's not their fault if their mum doesn't wash their uniform or brush their hair)
Smiley and approachable, with good people skills. I'm amazed at the number of heads I've come across who lack good people skills.
They should be hands on with the children, and I don't mean just telling off naughty children who are sent to the heads office. I would have huge respect if a HT ever got down on the carpet with the children in a reception class, even for five minutes.
They should be enthusiastic. About everything. 
They should have a vision, and SHARE this vision with the parents and children.
One lovely HT my DS had was very forgiving. No matter what DS did, after being told off/punished he was always told "Tomorrow is another day. We will start again in the morning." I cried when he retired. 