Not everybody wants to take the long journey of being able to sight-read extremely well. There are arguments for and against this but in this post, I'll focus on why you don't need to... because you have an ear!
If you've followed my content for a while, you'll know I always talk about mind first and mention the following concepts: internal piano, internal jukebox and internal manuscript. The second one is of interest to us in this article.
Once you have chosen your song (I demonstrate this on my channel using Blue Danube over three video parts, see below), find the original and listen to it many times. You want to get familiar with the structure, the melody, the chord changes and when they happen, as well as little musical subtleties such as slight melody differences the second time round, or a major instead of minor chord as it was previously, etc.
Water Pianism Syllabus Overview Document
Then, if there are lyrics, learn these too. They help with how the melody goes and remind you of the structure of the song.
Finally, listen to other versions of the song being played on different instruments and/or in different genres. This will show you what's possible with the song when it comes to your own personalisation efforts once you've learn it.
All the above is 'away from the piano'. Only once the song is firmly on your internal jukebox should you then go to the piano and begin by identifying the key (if you don't have perfect pitch, like me, simply play the song and find the key). No sheet-music is allowed in this process because it's an ear-training activity!
Once the key is established, expect 95%+ of the melody to fall on the notes of the major scale (one of many reasons why major scale mastery is so important; for orientation too). Now, knowing that you know the structure, start to play the piece's first section and refine it as you identify its path through the major scale, noting any 'out of key' notes. In Blue Danube, I play it in Eb (original is in E, you can change it if you want), there is a common out of key note which is B but we get the occasional A, too. The rest is notes of Eb, as expected.
Now that you've identified this melody section, it's chords time! This requires first and foremost an ability to recognise/feel the difference between major and minor-based chords, since all other chords (apart from sus4/2) are major or minor-based, no matter how fancy and complex they can become. Since you know the song so well on your internal jukebox, you should be able to identify the first chord at least then, applying some theory, you should expect the next chord each time to be either 'up a fourth' (C to F for example), or following the 251 progression (which is up a fourth movement in itself actually), as well as when the chord should be major or minor (2 3 6 are minor, 1 4 5 are major, 7 is half diminished).
You'd be surprised how easy this is because all the music from the last 200+ years is based on the same kinds of chord progressions: 1 4 5 / 6 2 5 1 / 1 5 6 4 / moving in 4ths / 2 5 1s which don't land on the root (I call these 'floating 2 5 1s), etc. There's rarely anything super 'out there'. Blue Danube is mainly 1 and 5, with 2 5 1s in there and a 4 here and there. All easy to identify. Plus, because you're playing by ear from your internal piano and not listening to the piece live, you can use some trial and error and you'll know instantly which chord works.
As you work through the song, by all means take notes which can help to recognise chord progression patterns and sections. Eventually, you will have played through it so many times that you no longer need the notes! This is the aim and is how I've learnt Blue Danube.
Eventually, you'll want to personalise it, I assume (otherwise you would have learnt it note for note from the original score!) Personalisation means there are no rules. You can slightly change the melody (there's one part in BD which I really prefer my way for the out of key notes, which is highlight in Part 3 - coming very soon at the time of writing). I also don't like Waltzes as a time signature so I'd rather play this either free-style, with no timing, just a nice melody and chord exploration, or as a slow, bluesy swing, which is totally my thing. Nobody will crack a ruler over your hands for experimenting and personalising! There's enough people who play all the classical repertoire note for note; we've heard Chopin played a billion times already. I think it's time for some modernised personalisations, don't you?
Good luck!
