Make your jam social! If you have some other people willing to join you, have them join
Have everyone keep the same steady beat with their feet
Take turns clapping different rhythms over the beat
If you want to get more advanced you can do the following
Keep the steady beat going with everyone’s feet
Each time when someone starts clapping a rhythm over the beat, keep that rhythm going
The next person can then add their rhythm on top of the beat and first rhythm
Keep doing this to see how many different layers of rhythms you can do at the same time
Have some instruments you can use?
If you have access to some instruments, you can try the jam with some people playing some basic rhythmic or melodic patterns on your instruments while others keep the beat on their feet.
You can also layer in some people clapping rhythms on top of the beat while others layer in some rhythmic and melodic patterns on their instruments.
See how many layers you can add before it no longer sounds good.