In accepting an offer, ask for it to be put in writing. Most employers feel it’s a reasonable request.
After you’ve accepted the offer, phone or write a thank-you letter to your network, contacts, and references, but be careful on its timing. If your decision to take this job was shaky, hold off thanking people for a few weeks. In case you leave this job in a short time, as occasionally happens, you may want to be able to act as though your job
search is continuing without interruption. Obviously, after you accept one offer, you have to turn down the others. If your final decision was difficult, turn down the other offers in a way that gives you the best chance of retrieving the offer later if necessary. Explain to each company that your rejecting it was a very, very hard decision because you were impressed with the company and the job offer, but you finally decided to accept this other offer for personal or logistical reasons, such as not having to move or requiring too much or not enough travel.