One person spins the wheel and whatever "rule" emerges the ensemble follows. Spinner may also write the rule largely on a white board, or alternatively, hold up a large card with the choice revealed.
CHOICES:
voices only
pentatonic
no key
major key
minor key
melody
refrain
recitative
percussion
whole notes please
low as you can go
softly
classic-ish
romantic
12-tone
minimal
show biz
folk
funk
freaky
left
right
center
bulbous
zapparific
horns to the moon
marching band
polka
reggae
tough
genre bending