Resignation Conversation

I let my manager know that I received another opportunity via email because I wanted to discuss the resignation further in our upcoming meeting. He wants to speak on the phone before then. I'm looking for general advice on how to approach the situation. There's no way I'd accept a counter offer because I'm hopefully going to my dream employer. I'm sure he'll ask why and where. I don't have anything against my current employer, I'm just want to move onto something else while I'm young and able to move freely. Any tips? This is my first resignation ever but I was one of the first employees in this section of my department.

Thanks in advance!

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