Ask thought problems, how would you do this and why. Even ask real problems that you're facing. Another really good indicator is whether someone can teach them

Ask thought problems, how would you do this and why. Even ask real problems that you're facing. Another really good indicator is whether someone can teach themselves a skill or talent. Did a business major learn programming on his own? Does a programmer read about business and gain a grasp of the subject? I always value 'doers' far more than 'thinkers' is someone willing to take action to fix a problem, not just think about it and then ask permission out of fear of being wrong. If someone has a highly analytical mind with developed problem solving abilities there are few problems they can't overcome. Another that I don't think people focus on much is, does this person's personality meld with mine and the rest of the team. In a startup you're going to be spending a ton of time with them, it's far more enjoyable and stress free if everyone gets along.