I know this might be a weird question, but bear with me. Recently I've been listening and analyzing Elton John's songs. I really loved the songwriting, chord progressions and chord voicing. In an interview Elton said that being a classically trained musician is the reason for his unique songwriting and chord progressions. So what do i have to Study/pay attention to while studying classical music to improve my songwriting, Chord progressions/Voicing. Or apart from classical music what do i have to study in general. Thank you in advance! P.s.: If anyone would suggest books or courses that would be great but please be free or inexpensive :)
By "unique" chord progressions, I would argue that he's saying that they're unique in comparison to other rock musicians. Because most of his progressions are, frankly, relative "classical" in nature.
And so this is the trick: knowing that Elton is a classically trained musician, study some of the music that he would have studied to get a sense of chord progressions that would have inspired him.
As a very famous example of this, consider the opening prelude to Bach's Well-Tempered Clavier. The first four chords are C, Dm/C, G7/B, C. (Or I–ii42–V65–I in Roman-numeral notation.)
Now, consider the beginning of the vocal part in "Circle of Life." It's in B♭ major, but you'll notice that he uses the exact same chords as the Bach prelude, just transposed down a whole step: B♭, Cm/B♭, F7/A, B♭. (And I've always wondered whether there's poetic intent here: this is often one of the first Bach pieces a pianist will learn, and it accompanies the text of "from the day we arrive on the planet.")
If you ask me, there's no way this is mere coincidence; every pianist of his stature knows that Bach prelude and what these opening chords are. He did this intentionally.
So keep studying music like this: find famous works for piano, and perhaps especially see what pieces he lists as personal favorites. Study "classical" music theory to get a sense of those chord progressions, and you'll be on your way to mimicking his style.