The first and most important skill is the emergency dismount. How to run out of the fall before becoming totally out of control. Elegant dismounts come much later. I recommend starting on grass. They won’t get half a revolution at first so the difficulty of riding on grass is irrelevant and it is a lot softer. Once they learn to do a couple of revolutions and can get off safely then move to a hard flat surface which will seem so easy after their initial attempts on grass.
Holding onto things teaches clinging. Spend no more than a few minutes getting the feeling of the unicycle while holding something so they know how to steer with pressure on the nose of the saddle from their thighs.. Get away from walls and ride into the open from a backstop that prevents the wheel rolling backwards. Put pressure on the rear pedal, lean both the rider and unicycle as far forward as possible, step up with the other foot and rapidly bring the unicycle up to speed.
Do not try to be too upright. The main balance technique is to pivot at the hips, keeping the unicycle wheel under the rider’s centre of gravity. Think of the unicycle as part of your legs and pivot the upper body at the hips. Controlling the wheel speed is also part of it but a novice can’t respond fast enough.
Pivoting at the hips is similar to what a child does when they first learn to stand. Adults do it too but the movements are so tiny as to be imperceptible.
Do you know anyone who learned to ride a bicycle by first learning how to still stand? Like a bike, a unicycle is easier to ride when it is moving at a considerable speed. Mounting is an advanced skill. Learn how to ride first by steering the unicycle towards the direction the rider is falling. (Also the same a bicycle.)
The mantra, "put the wheel where you would put your foot when walking can help some novices.