When pianists begin to learn a new piece, one aspect that consumes a lot of their attention is the whole matter of fingering. Many jazz pianists who play more by raw instinct perhaps do not worry about it, and simply let the the hands find their own way, so to speak, without planning it all out. But aspiring classical pianists and students of the piano, in my view, have a great deal of misunderstanding about the whole issue of fingering, which often prevents them from developing really strong technique.
You have read in my previous posts that I believe many ideas about piano technique were formed in the early days of the piano, when the piano literature was quite limited in its technical demands, the pianos themselves were quite different, and real knowledge about the physical actions of our bodies and how they produce sounds was virtually non-existent. The pieces of this era were what I would call quite "finger-y," in that they have a lot of scale passages, Alberti basses (simple broken chord patterns for the left hand), and simple melodies that span only a small section of the keyboard. Those pieces did not have the sweeping arpeggios, lush chords, and booming octaves that came later with Beethoven, Chopin, Liszt, and Brahms, to name just a few. These demand an entirely different type of technique, based more on the arm. To focus on "fingering" is to approach it backwards, in my opinion.
When I begin to learn a new piece, I do an outline (see my previous post on this topic). I don't worry about deciding on fingering at all at this stage. Doing a broad sketch of the piece gives me the lay of the land; I start to know where my hands and arms need to be from moment to moment. Where my hands need to be reflects the phrasing. A passage which is a single phrase needs to be connected by long continuous movements of the arm. When a new phrase begins, the arm moves to it as naturally as you would breathe between phrases of a song. In fact, the analogy of the song and breathing is very useful to learning to play with beautiful phrasing.
As I start to fill in more detail in the outline, more detail will also come regarding the exact placement of the hand from passage to passage, measure to measure, and that will determine the fingering.
Fingering is not a "one-size-fits-all." The size and shape of each pianist's hands will make some fingerings more comfortable and others more awkward. You must develop a keen awareness of what is comfortable for your hands. I believe it is a big mistake to blindly follow the fingerings written in the musical scores, which so many students try to do. These are just one person's opinion. You do not know if that person's hands were anything like your own. You don't even really know how successful that person was at playing the piece! In most cases, the fingerings you see are put in by an editor, and not by the composer. Even if they are put in by the composer, there is no reason to assume that there is only one way to play the piece. You must find what works for you. Therefore, I suggest buying unedited versions of the music whenever possible. If the fingering is written in, either ignore it or even white it out. If a passage in the music is particularly tricky and you need to decide in more detail how you will manage it, you can write in a few finger numbers here and there, which essentially remind you of how you will transition from place to place to accomplish the passage. The rest of the fingering will be obvious and you shouldn't need to write every finger used for every note.
There are also a number of myths and arbitrary rules about fingering, such as avoiding thumbs on black keys. This is absolutely ridiculous. Try playing Chopin's "Black Key Etude" or Debussy's "Clair du Lune" without putting your thumbs on any black keys! Again this idea took hold in the early days, and may have worked for the simple music of Clementi, or even Mozart, but certainly cannot work for most of the repertoire now. I have seen people come up with bizarre, uncomfortable positions for the hand and go through all sorts of gyrations just to avoid thumbs on black keys. If your overall use of your arms, hands and fingers is based on real, solid principles, you can use almost any fingering and make something work. For example, I can play any and all scales with the same fingering you would use for the C scale (1,2,3,1,2,3,4,5); therefore, in the scale of B-flat, my thumb will fall on both black keys, the B-flat and the E-flat. I can do this, with great speed and absolute smoothness, because I don't do the traditional crossing the thumb under. Instead I employ a very quick arm movement and can transfer from one hand position to another, anywhere on the keyboard, with speed, accuracy, and perhaps most important, no strain on the hand. Researching this topic I have found several references to the fact that Liszt used this technique and Chopin taught it as well. The whole matter of crossing the thumb under, or crossing fingers in general, is often badly taught, badly applied, and creates more problems than it solves.
With a solid understanding of technique and a teacher who can help you develop your technique, you will have many more tools in your toolbox than just the old ideas about good fingering. Again I would point you to Abby Whiteside's seminal book, The Indispensables of Piano Playing.