Note: I vote Republican across the board. So whomever goes up against Hillary Clinton will get my vote, despite not liking Trump or Cruz. The answers below relate to my Presidential primary vote. However, they follow closely what I use for local and state election as well.
I look for the following traits:
1. Experience - Has the person been a governor, or elected to another office of significance? Having a blend of state and federal experience is a major plus. Being a governor of a populous state for at least 2 terms shows that he/she can get elected. I'm thinking of states like Ohio, Florida, Pennsylvania, Michigan and Texas. Some of the decisions and events that occur in those state ca mirror those at the federal level, such as emergencies and budget issues.
2. Pragmatism - Someone driven exclusively by ideology will not be successful, for the most part. I would say that President Obama has largely been able to get his way ideologically, due to a compliant press corps. But overall, it is unusual. Events usually drive the Presidency. So looking for the best way to get something done, or at least the ability to negotiate, is vital.
3. Electability - I want to win. Even if I don't agree with the candidate on everything, if they are more electable in the general election, he/she gets my primary vote.