You set up a steady pulse, counting to four.
Once it is going well, everyone has to do a wiggle on count 1. That’s it. Simple.
Or do the wiggle on count something else.
Or have two actions, on different counts.
Or play their instrument on the count.
Or play instruments on one count and do an action on another.
Or divide into groups, each with their own count and action or instrument.
Or count to eight instead. I think you’ve got the idea!