Good communication is hard to categorize. Different people will respond to different social cues. In order to have good communication skills, you need to be able to adapt to different personalities.
I like what the other commenters said about listening, and responding with relevant and insightful material, this is obviously a pillar of good communication.
There are so many ways to get your points, or questions, or requests across to the people you are trying to communicate with. In general, look people in the eye, don't interrupt them when they are speaking, and listen with the intent to understand, then it will be easier to respond with something of value to add to the conversation.
In an interview, get them to explain a very simple concept to you. If they can explain the simple concept well, chances are they are articulate how a more complex system works. Asking your candidate to walk you through a solution or a system, will force them to use their vocabulary, and maintain your attention.
Cheers.