I am not sure why three is the magic number, but other than a bad work history (e.g., many jobs over a short period with inadequate or implausible explanations for each move) you need to establish traits that you see in people who are already doing the job successfully and emulate those while avoiding traits that would not work well for that particular job. For example, a sales professional needs to be assertive, confident and have a winning personality. An accountant . . . not so much.
I ask questions like, “What in the work place makes you angry?” If they say that nothing does, chances are that they are disingenuous. If they tell you what does, and it is believable and not objectionable to you, that is good information to know about the candidate.
If you ask in what areas they can improve and they cannot think of any, that is a red flag. We can all improve; and if a job candidate does not think so, don’t hire him or her.
It is also good to explore their ethics with a question like, “Have you ever faced a significant ethical problem at work? How did you handle it?” Another good one: "How would your last manager describe your attendance record and work ethic?” Watch his eyes as he answers. Does he hesitate?
Also, if a job candidate criticizes past managers or employers, think what she might be telling someone about you in a few months at another job interview.