If you are going to communicate something that is difficult or the other person will be resistant to, it is important to make a comfortable environment to support the other person (or yourself!). Deliberately scheduling time and taking the phone off the hook and arranging that there won't be interruptions are things you may wish to do.
The advice in this thread assumes that everybody communicating are honest agents, who WANT to clearly communicate. Occasionally you run into those who do not want clear communication - they are running their own agenda. The formal communication techniques described above in the post above can help to smoke them out. If someone never seems to have time for these clear, formal communication techniques - or they always prefer their own style (which never quite seems to get to the important things you want to talk about) then it would raise big warning flags with me. You may want to consider if you wish to remain close to them.
Warm regards, Rick.