Question:
Is there any exercizes I can do to INCREASE my skill in something? Or should I just keep playing music at my level and every so often a hard piece that takes a lot of practice to do.
Yes, there are lots of things (including exercises) that will increase your skill in something. However, you must be specific about what that something actually is.
Piano technique is like fitness. You cannot be fit for everything. You have to decide before hand what you want to be fit for, and then go through a programme of exercises for that end. For instance, in order to be fit for mountain climbing, you need a quite different set of procedures than if you want to be fit for playing football. Even within similar sports, being ultra fit at one is not assurance that you will be able to cope with another. I have seen amongst martial artists ultra fit karate people who were panting and dying after 10 minutes of judo training (and by the way, the reverse is true). Can you be fit for both? Yes, but you will have to practise both.
So, there is no need for confusion. Simply there is no general set of procedures that will make you technically proficient in general – although many piano pedagogues have been searching for this particular holy grail since the piano was invented.
At the same time you must not fall into the opposite trap which is to think that you are going to get fit for tennis simply by playing tennis – you will not, and you will end up injured. Likewise, you will not develop the technique to play a piece simply by playing it. You must first get the technique (but now you have a definite aim and the technique will be specifically designed to get you there).
My suggestion is that you choose a number of pieces that you want to have in your (future) repertory – no matter how easy or difficult – and ask your teacher to provide you with a gradual program to get you there.
Also have a look here (and if you feel like it, in my other 1500 plus posts – I keep talking about this in different guises) for my personal opinion about Hanon and Czerny:
https://www.pianoforum.net/cgi-bin/yabb/YaBB.cgi?board=stud;action=display;num=1084072922;start=9(Replies 7, 9)
Best wishes,
Bernhard.