Are you a good communicator?

I went to my doctor's office the other day. I walked in behind a gentleman who opened the door for me since I was pushing my daughter in a stroller. The receptionist behind the counter looked at me and suddenly said "Go ahead." while gesturing toward the other counter where the man had gone. I must have given her a confused look because she followed up with, "You're with him, right?"

"No," I replied. I went closer to her counter and she gave me a somewhat blank look.
"I have an appointment." I began.
"Oh, I was just trying to figure out if you were here for the flu clinic."
"No, but I should get a flu shot actually.... My appointment is [blah blah blah]."

This was, in my mind, an unacceptable exchange. A good communicator (and good customer service worker) would have just said something like, "Hello, may I help you?" Then this whole bizarre and confusing situation could have been avoided and gone much more smoothly.

At the same time that I was having a hard time with the receptionist, another man was having a hard time checking out.
"Do you have a co-pay, sir?" the check-out woman asked.
The man was confused, so eventually the check-out woman asked to see his card.
"It says here that you have a $15 co-pay." she stated.
The man said something like, "Oh, ok. Do you want it now?"
"Yes, you have a $15 co-pay, it says so right here on your card."

This same exchange repeated about three times. The man was clearly still confused, but each time the only thing the check-out woman changed was the tone of her voice which was increasingly annoyed. She even gave a wary look over to the receptionist and I and her eyes were saying this guy is an idiot. Finally she curtly explained "Yes, I need it now. That's what a co-pay is."

These are very specific examples and could be considered to be simple customer-service issues, but I've witnessed similar communication failures in personal/non-business conversations as well.

So, my conclusions are that to be a good communicator you have to:

1. Clearly state what your objective is. As I tell my son, "Use your words." Don't say partial phrases or give looks and body gestures and expect the other person to know what you want.

2. If someone doesn't understand you the first time, find a new way to say it. Saying the same words over and over in an increasingly annoyed/flabbergasted tone does nothing to help you or the poor, confused person you're trying to talk with. I remember doing exercises in middle school on things like this. People understand things in different ways, so sometimes you have to change your method in order to reach them. No excuses. Take initiative to be a good communicator.

These are just two examples I thought of. Do you have any other tips on how to be a good communicator?