Learning how to play piano beautifully requires constant work with both technique and expression.
But, being good at technique does not automatically make you play more beautiful, and playing with great expression does not necessarily mean that you can play very well technically.
If you want to play with expression- why do you need to practice piano technique?
Nobody likes a mechanical performance- no matter how technically impressive. The study of technique and expression never ends. You are never «done». It's a lifetime pursuit.
Ideally, technique and expression goes hand in hand all the time. However- as you learn how to play piano, you might get helped by working with different parts at first; like improving finger dexterity, coordination, dynamic expression, tempo, phrasing and articulation, etc.
Ultimately, by mastering all the nitty-bitty details, you will use this acquired «tool-kit» of skills in service of expression!
Studying piano technique is somewhat easier to show and teach.
Maybe that's why we piano teachers often tend to focus on it. Technique is more analytical, and more like a physical workout.
You can practice exercises, studies and various drills, as well as basic skills as scales, chords and piano arpeggios.
But even though it's possible to play technical exercises without feeling or even thinking, it's not recommended.
Try to play even a simple scale with thoughtfulness and beauty: Not because you have to, but because it sounds better, and keeps your inner «expressiveness» from hibernating...
(-Duh... of course you should play music with expression, otherwise it ain’t music...)
But it's amazing to hear so many pianists, struggling with difficult pieces, forget the cardinal rule of expression. Perhaps there are too many notes to think about, to have the time to describe or express anything...
Expression is something you have to dig deeper to get to.
No matter how well you play the music,
written or not, in regards to dynamics, phrasing, articulation etc., you still
have to put it all together in your soul, in your feelings. Otherwise it comes
out as fake.
So how can you practice expression?
Unless this is something that comes naturally to you, you need to discover it.
Everyone has a vast library of "expressional" qualities inside- you just need to find your way around this inner library and not being afraid or shy of letting your expression out.
But you also need to learn how to play piano and really listen; that what you want to express is also what can be heard!
What else can you do?
Because that's what music is. Expression. Feeling. Life. And utterly human...