1 Ability to lead 
2 Political Platform (Policies)
3 Track Record 
4 Social Awareness (probably evident in 2&3 (above))
5 Grasp of life's realities (As for 4)

A leader should have magnetism that attracts good people and inspires others to do good things.  Reagan, for all his failings, was inspirational.  Simplistic, but inspirational.  Jack Kennedy inspired the country to do great things.  No president in a long time has been able to harness our abilities and talents to address the issues in front of us.  We are fractured and scattered, and for the lack of good leadership, spend our time shouting at each other in the political arena.A leader needs depth, wisdom, gravitas,  We need to feel that things are under control.
A leader needs to be able to give us the bad news, and act accordingly regardless of how it will poll.  As Tom Friedman said in the NT Times today, we need someone who is not reading the polls, but is changing the polls.
Unfortunately, with the rabid politicos and pundits ready to assassinate the character of anyone who aspires to political office, wise men fear to tread.  Hence the fools we have leading us today.

Here in the USA we have little choice.  Leaders are largely chosen from a pool of those whose main qualification is a skill in raising money.  If we’re lucky one of the two final “choices “will have the qualities that we would like a leader to have.

Beyond that, there is another question.  Is leadership possible anymore?

Because of the utter complexity of our world the capacity to plan, organize, inspire and lead may be beyond us.  The scale and complexity is just too vast.  At hand at every moment is some random event waiting to happen to change everything, every plan on the cutting edge of obsolescence.