Fire fast!
Always keep this in mind. Take extra time in hiring people. I first heard this from Brian Tracy, a business consultant. Interview the person three times. Do it in three different environments. Do your research. And take your time.
The other part of the equation is to fire fast. What does that mean? The question to ask yourself is:
Knowing what I know now, would I hire this person again?
If the answer is no then FIRE THEM. And do it immediately.