Take turns freestyling in a whisper voice.
There are actually two kinds of whisper: a very quiet vocalized whisper, and a non-vocalized air whisper. In the vocalized whisper, you are still making sound with your vocal chords, but keeping it as quiet as you can. There’s a tendency to forget the point of this exercise when you get excited, and slowly increase the volume, so be careful. The vocalized whisper is easier to understand. The air whisper sound is made using the breath alone with only your mouth shaping the sound. It sounds more like a true whisper, but the words are harder to understand. The sound is all sibilance — that sort of hissing sound — which can be tricky to work well with a mic. Both styles can be useful, and some people will be better at one than the other.
This practice will develop your awareness of mic dynamics, taking note of and controlling your mic volume. It can help some people understand that they can be too loud on the mic. People who are too quiet most of the time might also benefit as they realize their normal style is actually a whisper. This practice also helps with clarity and enunciation, because if you can be understood in a whisper, you are probably articulating your words well. Whisper style can be effectively used for dramatic effect.