Try these ideas for fun, then compare ideas with your Uke friends:
Move a chord shape higher than usual. This is an interesting way to find new sounds. This is what we'll be doing with True Colours, for instance.
Play scale - leave out every other note. (Sing left out note in your head.)
Play Pentatonic scale - play every first note, sing every second note.
Play scale - jump up two notes, then back one, continue pattern.
Play scale with a friend - alternate notes.
Practise chords changing carefully to new chord, BUT keep strum going no matter what.
Teach someone in your house how to sing one of your uke class songs.
Call a relative on the phone and play them a tiny concert! (like your grandmother or a favourite cousin or aunt.)
Play two scales at once with your friend.
Try playing two scales at once by yourself.
Double Strum: how long can you do a steady double strum? 30 seconds? 40? A minute and a half? Longer?
Chord Drill with a Twist: pick the name note of a chord once, then strum it 7 times, pick name note of next chord, strum seven times, etc. Don't slow down your beat!