Making the bed is the standard example and it's slightly annoying because it works. Not the tidiness. The fact that something reached completion before eight in the morning.
One step is a deliberately low ask. Low asks still get done on the days that go wrong, and the days that go wrong are the ones deciding whether a habit survives at all.
Pick it now, before the day fills up. It should be small enough that skipping it would be faintly embarrassing.