How do you tell your boss that you are resigning when you know that it will come out of the blue?

Be honest and just say what you wrote in the details section of your question.  If your boss is a reasonable person and wants to maintain the relationship, he/she will shake your hand and wish you luck.

I am answering anonymously as I am about to engage on this path myself. I think the best approach is simply to follow protocol and submit a tactful and professional letter of resignation giving requisite notice; if one feels a particular need to set forth "reasons" (I am not yet decided on this, myself), they should be related to procedure, practice, or professional satisfaction with the position, not people, politics, or statements of personal preference. The implication that an employer "deserves" more than this is, to me, fallacious. To be sure, were the situations reversed and I were being laid-off or fired, the company would have no obligation but to inform me this is the case (and, in my experience, they rarely give the courtesy of personalizing or providing helpful insight/guidance on these things). I see no reason not to uphold that tenet myself.

Encounter this situation for few times, well currently i also wanted to give this news to my current boss, i can't sleep properly for about a week after i receive a confirmation to be employed by a bank. I was exited in taking that offer since i was in the same line with it before i enter this current company. I admit that i wasn't happy with my current company, not just the environment but also the attitude of coworker. I wasn't really concern about if i can get along with my superior or my coworker since i am an out going person to begin with, but how they backstabbing each other is the most concern-able issue. Before i walk to my boss room i went out to take some fresh air, and a cup of warm water to calm me down. Be prepared to answer few must question from your boss eg. "why are you resigning or can you consider to stay?" it's best for you to answer it sincerely if you really want to leave the company but still in a polite and professional manner. But if you still consider to stay with the company let you boss know about the changes that you want. If he offer to you as what you may need, you should consider about it. Make a brief explanation when you announcing your resignation to you boss eg. "Sir, i've been considering leaving the company, it's been hard for me to finally make this decision, and i would like to express my gratitude to you for letting me work with you." it is hard but just take a long breath before entering your boss room. Also take note if your boss is busy or not, this is a crucial thing that you need to really see in to, observe the situation before you tell the breaking news to your boss. Finally be confident with you decision.

Your manager is either going to get mad or he's not. You can't please everyone, nor should you live your life trying to. If you take these steps you'll be doing the best you can to maintain the relationship and increase his opinion of you. I would emphasize giving as much notice as possible (within reason) once you are 100% certain of your plans. 4 weeks is very generous. Don't give so much time that plans might change between that point and when you expect to leave. Help train other coworkers in what you do and document things as much as possible. Offer to be available on a consulting basis either for future projects or if they have any questions. Make sure your boss is aware he's not the reason that you're leaving. Most people quit their jobs because of their bosses. Tell him you really enjoyed working for him and would certainly be willing to do so in the future if the opportunity ever arises, but that you have an offer that you can't refuse - either because of the work, potential for career advancement, salary, or whatever.

You already said it... Right there in your question... Up until the point that you start talking about how upset your boss will be. Your boss either wants you to fulfill your long term career goals or they do not. If they can and will enable you to fulfill those goals in your current situation, then it would probably be a mistake to leave - but if they either cannot or will not, then you have no reason to stay or to apologize for pursuing other options. You've already gotten over the most difficult part of this negotiation: determining where you want to go and finding a path that will take you there. If you're not personally close enough to your boss to have been communicating the mismatch of your current job and your life goals all along, there is no reason to get worked up about it now, just as you're leaving. Tell him/her exactly what you said above, give an appropriate timeframe to close out your responsibilities and hand off projects, and go.

You request a meeting.  You say, "Working for you has been awesome.  You have been a great boss, but I have a job offer that I feel like I have to take.  If I could take one thing from this company it would be you.  I just wanted you to know that"Since you are worried about both his feelings and reputation, at least some of that's probably true.