Prepare for It. This one is easy. All you have to do is smile and say "Thank you so much for your support. I've enjoyed my time here and I've learned a lot from you. Let me know what I can do to make the transition easier." Are you always going to get reaction number five? Probably not. But if you look for the signs, you can likely anticipate your boss' response, go into the conversation prepared, and come out stronger on the other side. Then, you can breathe a sign of relief and start looking forward to starting your new position.
Your End Date. The most crucial detail in a resignation letter is your end date. Legally and according to your company's policy, you might be required to give a minimum amount of notice (two weeks, or possibly more, depending on the company and the role). If that's the case, you don't want there to be any confusion about how much notice you give. If it's right there in writing in a letter dated two weeks before your last day, you're saving yourself the hassle.