I have only been summoned to jury duty one time in my life, and I tried to postpone it by claiming my job was vitally important and no one else could replace me if I were asked to serve on a sequestered jury. They didn't believe me, so the request for postponement was denied. I heard from other people that it's nearly impossible to use employment as an excuse to postpone jury duty.
Fortunately for me, I was excused during the jury voir dire process. It was a case where the death penalty might be in play, and I told the attorneys and the judge that I could never sentence a person to death because it was morally wrong. The prosecutor excused me right away.