As often as we can. We got into the habit in our last place that had one shower that was literally so small, I could stand in the middle of it with my hands behind my head and touch each wall. The water heater wasn't much bigger. So if we wanted to each take a shower on the same day, it was either take them at least 6 hours apart, or take them together, since there wasn't enough hot water for 2 showers back to back, lol.
And even with as teeny tine as that shower was, we still
managed to find a way to get it on in there.