What I do is decide what policies I think are necessary, then I look at the track record as best I can of people who have the hubris/temerity/ego/money/support to run, and then see if I think they can #1 win and #2 carry out the agenda they have articulated.
That sounds like a simple 1 2 step but it is of course a conglomerated mess of impressions, feelings, experience, sensibility. This I do know: somebody is going to be the chief executive officer and I want someone who can function in that role and someone whose notion of what this country IS and NEEDS is somewhat compatible with my own. And I would like to steer between Mother Theresa and Tony Soprano, though Tony might do less real harm.