The trick to being a great conversationalist could be the 'best friend face'

You've probably heard before that one key to being a good conversationalist is letting the other person talk (and talk and talk). The better you are at listening, the more your conversation partner will like you.

This doesn't seem like the hardest thing in the world - just zip your lips and keep nodding. And yet too many people screw it up.

It's not necessarily that they're blabbing too much, either - it's that they look confused or disinterested while the other person is speaking.

That's according to Bill McGowan, an Emmy Award-winning journalist turned communications coach, whose trainees include Sheryl Sandberg and Jack Welch.

In his book, "Pitch Perfect: How to Say it Right the First Time, Every Time," co-written with Alisa Bowman, McGowan says he works with almost every single client on displaying an appropriate listening facial expression.

The authors write:

"Even those people who muster a certain level of enthusiasm while they're speaking will emotionally and expressly downshift when they become the listener.

"Their engagement seems to dissipate, or worse, the corners of their mouths turn down, they furrow their brow a bit and sometimes even squint their eyes: all completely natural things to do when we're concentrating hard on something.

"The problem is, to an audience or your conversation partner, that facial expression is usually interpreted, 'I haven't the slightest idea what you're talking about.'"

The facial expression you do want to display? It's what McGowan calls "best-friend face": "It's the curious expression we have on our faces when we are listening to our best friend tell us a great story. The perfect BFF is a quarter smile."

As in: You're smiling, but your mouth is closed, and you're not grinning like a maniac.

For most people, achieving that perfect BFF requires some effort. McGowan recommends displaying different facial expressions in the mirror until you find one that feels natural - and looks authentic.

McGowan often has his clients review freeze frames from TV interviews and analyze what their facial expression is communicating.

These insights shouldn't make you paranoid - your conversation partner will probably pick up on that, too. The goal here is really to "look just as curious when you're listening as when you're talking," as McGowan says.

So try to make the other person feel as comfortable as possible: Lean in, make eye contact, and relax your face. It sounds like a lot of work, but it gets easier over time, and brings with it the reward of more fulfilling interactions.