Whenever I hire someone, I look for two things: aptitude and attitude. I tell that to the interviewee pretty soon during the interview, too. That gives them an understanding of what I'm looking for. However, before you get to have a face-to-face with me, I've already had at least one phone interview with you - the in-person interview is just to confirm or change what I think I know about you.
Aptitude is the knowledge-base or skill-set that an employee brings with him or her. That is a compilation of that person's life experiences, education, work knowledge, training, books read, and everything else that this person has learned to this point in life. It is far too much to unpack in an interview but I try to get a glimpse into what the person knows.
Attitude is the mindset the person has about work, life, other people, etc. Attitude is BY FAR the most important of the two items I look for. I can train aptitude if you have the right attitude. Aptitude is easy and knowledge can be taught. Attitude can never be taught - it is who you are and tells me (the prospective employer) more about what kind of employee you'll be than any résumé ever will. Attitude comes through loud and clear usually within the first 60 seconds of a meeting, even an interview where you're doing all you can to impress someone.
This approach also works with both volunteers. Get vols who have the right attitude, and whatever program they're in will have a much better change of success. Having the right attitude to anything in life will infect and affect others around you. So, my suggestion is that when you interview for a staff position or a volunteer (or even when you interview somewhere) have the right attitude regardless of your aptitude. Eventually your attitude (and those whom you interview) will rise to surface - you might as well know it from the outset.