I'm not sure what you mean by the "ideal skill" unless you are referring to the ideal sequence of steps to follow when performing a skill for demo purposes? Start by taking each skill and write down a step by step "recipe" for yourself to complete that skill as if you are explaining it to a child. Something like:
1. Turn face towards students and point to mask skirt on face
2. Slightly lift skirt to flood mask partially with water
3. Face students and point to water level under eyes to show them mask is partially flooded
4. Hold out index&middle fingers to show students start of mask clearing procedure
5. Place index&middle fingers on top rim of mask; apply slight pressure
6. Inhale slowly through regulator
7. Look towards water surface at 45 degree angle
8. Exhale slowly through nose to clear mask.
9. Look to see there is no more water in the mask and show students with exaggerated movements that the mask no longer has any water in it.
10. Give OK signal
etc.etc.etc.
Do this for each of the 20 skills and then get in the pool and perform each of those steps slowly and deliberately exaggerate your movements - remember that what we think is clear to the student may not necessarily be so clear to them so make sure you check with them that they got the sequence and perform it twice or a third time if necessary. Demonstration quality means that it is smooth, appears uncomplicated, confident, comfortable, and demonstrates every step in the sequence clearly so a student who watches you perform the skill can see what they should do to complete the skill themselves.
As a DM you should have these skills down as second nature yourself so work on those you feel uncertain about (if any) until you can do them perfectly and effectively. One of the biggest things is to learn (and remember) to slow down your actions and exaggerate your movements a bit so students can clearly see
why it works when you do it.