Inexperienced improvisers need to realize that there is huge power in silence. Sometimes more can be communicated by what someone doesn't say instead of what they say.
People and Chairs recently posted about how to improvise without dialogue. In that article, they asked improv teacher David Razowsky about silent scenes. A couple of phrases stuck out in our minds:
When you consider that scenes aren't about what we say, rather they're about how we say it, then the world opens up for you.
The first line of dialogue isn't spoken - it's noticed.
A scene with no dialogue is the greatest expression of trust two or more actors can engage in.
The video excerpt below is taken from the TJ and Dave documentary Trust Us, This Is All Made Up. They start a scene in complete silence, for almost 14 seconds. Their scene then begins very gradually, even with the first lines of dialogue not revealing too much about what's going on in the scene. They show incredible trust in each other that eventually the point of the scene will manifest itself. Which is does, more than two minutes later.