The most important question you should ask yourself at the end of each interview is "Do I want this person on my team?" If you're not sure, the answer is no.

Aside from that, be wary of anyone who spends too much time talking up their accomplishments - I've often found that candidates who talk a lot falter when asked practical questions.

Also, make sure you leave time for the candidate to ask you questions. That portion of the interview can really reveal to both parties whether they would be a good fit.