It's easy: You: Boss, we need to talk. Boss: Ok, let's talk. You: I decided to leave ${CompanyName}. Boss: Ok, is there anything we can do to make you stay?

It's easy: You: Boss, we need to talk. Boss: Ok, let's talk. You: I decided to leave ${CompanyName}. Boss: Ok, is there anything we can do to make you stay? You: No, I've made my decision. How long do you want me to stay to transfer my responsibilities? Narrator's note: the standard is 2 weeks. Other things: they might ask you why you're leaving. It's not the time to provide them with a list of complaints (especially if you haven't raised them in the past). You can be vague but truthful: the other opportunity looks like a better fit for you. That is essentially the script I followed when leaving my past jobs. All my bosses were professional about it and understanding.