Four moves for the conversation itself, not a general essay on making the decision.
If you've been through a Performance Improvement Plan and you're here because the improvement didn't happen, you don't need another essay, you need the script. Use the Termination Conversation, Manager Template, and read the four moves below first, they're what to think about before you walk in.
Never get into an argument. If they push back or challenge the decision, don't defend it point by point. Restate that the decision is final and redirect to next steps, arguing implies the decision is still open, and it isn't.
Listen without engaging. Let them talk if they need to. Listening is not the same as negotiating, and it costs you nothing to hear them out.
Keep it short. The longer the meeting runs, the more room there is for it to go sideways. Ten to fifteen minutes is typical, say what needs to be said and hand off to HR.
Run the language by HR or legal beforehand. Don't freelance the wording on the reason for termination, especially anything protected-class adjacent, performance related, or involving a PIP. Have HR review your script before the meeting, not after.
Write it out ahead of time. Don't wing this one. Draft your actual lines in advance, review them with HR, and stick close to what you rehearsed. This isn't the conversation to improvise.