I'll second that. Being ready for the conversation is important. Because these kinds of conversations involve more sensitive matters, there are potentially bigger risks to normally small things like someone misunderstanding what is said, or being distracted, or just having a bad day.

I tend to be not so good at this, since if there's something that's really bothering me i'll often just let it out. Sometimes i'll remember to preface it with a check to see if my partner is ready to talk now. It doesn't take long for someone to become close enough to me that i'll just tell them whatever i'm thinking. I suppose the positive side of this is that you can have some confidence that i'm not secretly harbouring bad feelings.

Anyway, i'd say: make yourself a note, ask if your partner is ready, and if he is (or when he is), just start to explain what you're thinking about, with the note on hand in case you forget something. If you both really are ready, you won't have to worry about saying everything perfectly, because there will be plenty of time to work out together what each of you really have in mind.