To change things up at times for a client who is well conditioned I’ve done a rotating set. For example
Circuit 1: 15 squats & 15 biceps curls
Circuit 2: 15 biceps curls & 15 lunges
Circuit 3: 15 lunges & 15 medicine ball squat to overhead press
Circuit 4: 15 medicine ball squat to overhead press & 15 mountain climbers
etc. finish off with the last exercise being the first one you did
You can repeat the circuits as many times as needed.
It changes things up!