Preparation is the key to so many things in live. You wouldn’t give a critical presentation without having prepared. The same is true for a difficult conversation you may have to have with your manager or an employee.
Think carefully about your desired outcomes for the situation. Is there a particular behaviour that is getting in the way of your work? If so watch the behaviour of the other person for a while. Be sure you are able to describe what is not working for you in a calm professional way.
It is best if you can describe their behaviour as if you had captured it with your cell phone. Neutrally tell them what didn’t work in your last interaction and what would work better for you going forward. Then be prepared to listen carefully to what they have to say to be sure you hear their side of the story. Be prepared for different reactions including surprise, disbelief and anger. Being prepared will ensure you have the best conversation possible that will lead to a workable solution