Accepting a job offer is usually a final decision and a cause for celebration. In some cases, circumstances change unexpectedly after accepting a job offer, and it may be necessary to rescind an acceptance. Handling the situation with class and respect is the best way to avoid burning bridges.
Analyse your reasons for turning down the job offer. Your spouse may have got a promotion that requires your family to move out of the area. You may have received a better job offer, or you may have discovered a family circumstance, such as an illness, that will prevent you from devoting the necessary time and attention to your new position.
Draft a professional letter that explains your regret for not being able to accept the position and the reasons that you are not able to do so at this time. Thank the company for the opportunity they've offered you. Apologise for the inconveniences your inability to accept may have caused the organisation.
Arrange to meet with the hiring manager in person, or set up a time to speak over the phone. It's best to make a personal effort to deliver the news, because it makes you appear more genuine. Setting up a time to speak with the hiring manager will ensure that you are able to speak to him directly, rather than leaving a message on a voicemail or with a receptionist.
Express your sincerest apologies for having to turn down the job offer. Be as honest as you can about the reasons why you're not able to accept the position, without being offensive. If you have accepted an offer from a competing company, mention that you've accepted another offer that you can't refuse, but don't mention the company's name.
Express your gratitude for being given the opportunity, and your desire to keep the lines of communication open for future opportunities. Never close the door on working with the company in the future. The organisation obviously saw value in your talents, and there may be another position you'd like to apply for someday.
Deliver the letter you have written to the hiring manager during your face-to-face meeting, if you have arranged one. If you end up speaking to him over the phone, hand deliver the letter to his office within a few days after the discussion. Send copies of the letter to any other parties involved in the hiring process, with a personal note attached to each thanking the person for her role in offering you this incredible opportunity.
Sending a small flower arrangement or fruit basket as a token of thanks may help to smooth over any negative feelings.