Mind first, mind second, mind third.
No matter if you have problems including scale fingering, memory, chord visualisation, key recognition, rhythm production or piece interpretation, the solution to your problem lies much closer and is far more accessible to you than books, teachers, repetition, force and guesswork.
The solution for each problem mentioned above, and any other, is not something that is found; rather, it is revealed to you in moments of silence and patience away from the piano.
Due to the ego, we demand answers and have created a culture of immediacy in our endeavours which result in nothing but frustration, failure and unnecessary comparison with others. A heavy price to pay when all one need do is settle down in silence to promote patience and thus open up that place in which answers may be provided.
Before such a practice is employed, it is very important to first accept that this silence is indeed the only way you will achieve a sense of success in your playing and pianistic ambitions. Until that time comes, which will indeed come at the right time, your ego will continue to doubt, force and attempt to be in control of your perceived progress, also rejecting the content of this article. Immediate results will be expected through pained, futile repetition, yet they will not come for the simple reason that the mind is not still.
The only prerequisite to the following guidance is to have solely one question in mind upon which your moment of silence and patience shall be based. This helps to clear the mind from clutter and provide a more specific response to your issue.
It must be understood that the answers to the problems you believe you have are already within you; your body and mind are entirely able to finger scales correctly, memorise pieces and identify keys instantly. What is stopping you is what I call 'conscience interference'; this can only be diminished through regular periods of silence. The natural state of water is stillness; when in this state, one is able to see far deeper into it than if it is in motion. Such is your mind.
Let's consider a first issue: scale fingering. You have spent many hours and had many discussions with your teacher, read many websites and watched many videos, yet you still find quite a lot of the major scales quite difficult to play correctly using both hands simultaneously or you lack speed and fluidity.
As already mentioned, your fingers are already perfectly able to perform as required; the problem is that they are not performing as desired, and herein lies the root of the problem: Desire is a component of conscience interference. By over-analysing, over-practising and over-thinking, you will only block the readily available channel between your naturally still-natured mind (which is current not still) and your fingers, rendering accurate, satisfactory execution impossible.
An almost vomit-inducing response to such a dilemma is, "My fingers can't move fast enough". They indeed can move fast enough but the reason they do not move fast enough is because you 'desire' them to move faster than they currently are able to due to your ego's desire to go faster and have this demand served up immediately. Grasping water causes it to leak from between your fingers; holding it without force, it remains.
By learning to sit in silence to instil the much-neglected value of patience, you will train your mind to ignore your ego and to work at a more natural pace, little by little increasing as your mind and body see fit. Do not forget that You are not playing, you are being played, so any failure, as you may consider it so, is simply what your mind and body are currently able to do and are not failures at all.
By blending playing into practice and practice into playing, your previously incorrect assumption that practice improved playing will disappear and everything you do will be both a performance and practice, a 'practormance', so to speak.
Whilst sitting, pose yourself the question that you wish to have answered by your mind: "My scale fingering is currently not satisfactory to me, how may I improve myself?" The answer, tailored only to you, will begin to reveal itself thanks to the mental decluttering taking pace as it has never done before. What you will find is that you will visualise the piano keys, see a particular major scale and sense the signals moving to the associated fingers without actually moving those fingers.
Since every hand is different, your fingering may well be different to your teacher, a book or even a YouTube video you have seen. So be it. Your fingering has been provided to you, and that is what your mind knows already is most suited to your particular hands. Accept this.
Once you return to the piano, you will find that what you thought about and discovered during your moment of silence will come out instantly for what you play on the piano anyway comes from the mind; people seem to think muscle memory means 'memory of the muscles' whereas in fact it has nothing to do with muscles at all, they simply receive the signal from the mind which has internalised a particular pattern through repetition and so could be played in your mind with your eyes closed away from the piano without your fingers moving at all since it is so engrained within.
Do please stop using the term 'muscle memory' and furthermore do not strive to 'achieve it'. Muscle memory is not an honest performance, it is an artificial replica and no more impressive than an animal learning that to get food, a bell must be rung.
To take a final example from the potential difficulties noted in the opening paragraph, rhythm is oft-times a difficult one. Hopefully by now, it is understood why it is a difficulty for some? It is indeed because of conscience interference.
If you ask any improvising musician of any instrument what is being thought about whilst playing, the answer will be the same: nothing. Even non-experienced musicians have examples from life outside of music whereby something is executed so easily, such as making dinner or driving a manual car; conscious thought is not given to the dangers of the road ahead, which gear to be in, which direction to go to get home, etc., it all simply happens subconsciously without much conscious thought yet. Such must be your mind at the piano.
Rhythm must not be analysed, it must be experienced and felt. Rhythm need not be 'heard', since it can be demonstrated by striking the fingers upon one's body, for instance, and counting the beat to the confused learner. By asking the 'student' to close their eyes and then tapping the rhythm on their body as you count, eventually, they will tap their foot in time. This is how rhythm is internalised without any conscious interference.
Once understood, the learner should be encouraged to have a silent moment and allow the feeling of that rhythm to play itself in the mind over and over again. This can be enhanced by seeing their 'internal piano' as I call it, and playing a particular known piece in this new rhythm. Very soon, the rhythm will be instantaneously performable at all times.
And so the examples go on...
Having taking the time to read this article, I do hope you will take away the practice recommended and apply it to your own problems. By first accepting that everything takes place in the mind and that the body follows, then realising that you already possess the answers and ability within, that they are just blocked by the un-still mind and that through practising silence and patience, you will surely make progress that will be very natural and which will require no ego demands or desires.
Remember: Play You.