In six not so easy steps:
Accept that it’s not going to be pleasant. Lots of things are difficult and unpleasant. Influenza. Traffic court. Surgery. Unlike influenza, a difficult conversation is never fatal. You are strong enough to survive 20-30 minutes of something very hard. Stop looking for the magic easy way to have the conversation, because that way does not exist.
Know what you want from the conversation. We tend to focus on what we want to say, but that is not the important part. The important part is the outcome we’re seeking. Identify the result you want from the difficult conversation. Write that down so you can keep it fixed in your mind.
Set the stage. Find the time and place to have the conversation. Do not just catch someone out of the blue. Ask for a moment of their time. If they’re not free now, set a time you can sit down together.
Start the conversation clearly. I like to start with “I need to have a difficult conversation.” It helps me feel less awkward and lets the other person know they’re not imagining the tension.
Stick to the facts. Be as clear and unemotional as you can be, and focus on the facts on the situation. “Uncle Joe, I need you to stop borrowing my snowshoes without asking. Last week I was stuck in the cabin for three hours because you took the snowshoes unexpectedly. I am happy to loan them to you, but I need advance notice so that I can get the snowmobile ready in case I need transport.”
Thank them. If the conversation goes well, thank them at the end.
Important caveat: if your loved one has dementia, or a form of mental illness, or is a total jerk/creep/monster, this is not going to work. They will not respond in predictable ways. You can still try, but doing everything right isn’t like to get you better results than any other approach. You’re pretty much stuck on step 1 in that case: accept it will be unpleasant, and give it a try anyway.