I went through a several teachers when I began lessons at 9. With slight variations they assigned me scales and arpeggios ( which I still hate) Czerny and Burgmuller. Then a horrible period with Pischna and Plaidy. One of my earliest teachers had me sitting at a table with my hand resting like paws ... then she instructed me to lift each finger one by one and tap the table. I hated that too.
When I was fifteen I met Madame Kolessa .. a retired European concert pianist By then I was a student at the Quebec Conservatoire and very advanced. Well she told me outright I'd do nothing but technical exercises for SIX months ... two or three hours a day. She was testing my determination and preparing me for the most incredible technical exercises I ever learned.
The first lesson ... she grabbed my arm and suspended it over the keys and growled ..?Relax" ... after considerable growling I finally attained the appropriate relaxed weight ... whereupon she dropped my arm onto the keyboard. The resounding crash still reverberates in my ears forty years later. The torture continued. I was required to relax and then drop onto the keys. Stiffening a finger could easily have resulted in a broken digit but she made sure my wrists were limp before the plunge. And when my hand hit the keyboard the entire wrist dropped below the level of the keys. It was arduous and painful. I had bruises on my wrists from "misses".
But in six months I had a technique which was the perfect vehicle for hours of heavy practice ... and which allowed me to play with the flourishes of a concert artist. I could raise my hands very high off the keys and hit those chords unerringly. Someone recently remarked that my relaxed hands look eerily boneless .. like an octopus ... and I realized that they do. I type a great deal as well and have never suffered any join pains .... because I drop onto everything. There is no"rigid" position ... I flap and flutter over the keys of both the piano and my computer.
So while I don't impose such a rigorous regimen on my students ... I do insist that they relax those hands. My only insistence on "form" is that they make "paws" ... gently curving the hand. Dexterity is provided by practicing the scales and the Hanon .... but again ... always in a relaxed state. If they stiffen up then I have them shake their hands vigorously for a few moments. I don't fret over body position or arm position ... if the shoulders are relaxed. then they won't be hunched up around the neck.
Relaxation is the key. Consciously relax your fingers and feel the difference. I wouldn't suggest dropping your arms onto the keys without a good teacher beside you. But you can practice lightly bouncing off the keys an inch or so to get the feeling.
There is far too much emphasis on body posture and finger positiong and so many details which far too often serve to make the students terribly tense. The first rule is to RELAX your fingers ... and then the arms and upper body ....
If you want a free download of Hanon, you can get one at IMSLP ... or my website. I recommend it because it's easy and fun and a great workout .... if you relax before each bar. And it contributes to dexterity.
Lubka Kolessa has several You Tube clips but none show her playing ... they are all recordings. But you can hear the fluidity of her touch. 
