We must understand what technique is because not understanding technique leads to incorrect practice methods. More importantly, a proper understanding can help us to develop correct practice methods.
Technique is the ability to execute a zillion different piano passages; therefore it is not dexterity,
but an aggregate of many skills.
We must understand our own anatomy and learn how to discover and acquire the correct technique. This turns out to be an nearly impossible task for the average human brain unless you dedicate your entire life to it from childhood. Even then, most will not succeed. The reason is that, without proper instruction, the pianist must discover the correct motions, etc., by trial and error.
The basic keystroke must be learned by every pianist. Without it, nothing else will make a meaningful difference – you can’t build a Taj Mahal out of mud-bricks and straw. The keystroke consists of 3 main components, the downstroke, the hold, and the lift. This might sound like a trivially simple thing to learn, but it is not, and most piano teachers struggle to teach their students the correct keystroke.
Long before their first piano lesson, you can show children pictures of enlarged music notes (tadpoles!) and familiarize them with the music staff, where the notes go, and where to find them on the piano. This will simplify the teacher’s task of teaching them how to read music. If you are not a pianist, you can take piano lessons at the same time as your child; this is one of the best ways to get them started.
Without performance training, even good performers will not perform to their best ability, and the majority of students will end up thinking that piano performance as a kind of hell that is associated with music or piano. Once that attitude is ingrained in youth, they will carry it into adulthood. The truth should be the exact opposite. Performance should be the final goal, the final reward for all the hard work.
The human brain can be quite wasteful. For even the simplest tasks, the untrained brain uses most of the muscles in the body. And if the task is difficult, the brain tends to lock the entire body in a mass of tensed muscles. In order to relax, you must make a conscious effort to shut down all unnecessary muscles. This is not easy because it goes against the natural tendencies of the brain. You need to practice relaxation just as much as moving the fingers to play the keys. Relaxing does not mean to "let go of all muscles"; it means that the unnecessary ones are relaxed even when the necessary ones are working full tilt, which is a coordination skill that requires a lot of practice.
In summary, beginners who have never touched pianos or portable keyboards previously will need to develop their stamina gradually because piano practice is strenuous work. Parents must be careful about the practice time of very young beginners and allow them to quit or take a rest when they get tired (about 10-15 min.). Never allow a sick child to practice piano, even easy pieces,because of the risk of aggravating the illness and of brain damage. At any skill level, we all have more muscle than we need to play the piano pieces at our level.