You had mentioned "form" when we met on Sat.
A great book on this is Schoenberg's "Fundamentals of Music Composition" which I've had for years and is also good for thematic development.
I'm not suggesting you buy it but it's good even though it's as old as the hills.
Most extended form (Sonata-Allegro /Rondo / others) basically boils down to song form (binary/ternary). I've told students for years if you can't write a 2 part song don't take on extended forms. For film type work a good knowledge of song form is probably sufficient.
Classical song form is basically what we call A/B form or in ternary some use C or A1. Good examples are Schubert Art Songs though the form is based on the poetry.
Popular music songs of the 20s through 70s were predominantly A/B form including the Beatles, Motown and others. There are always variants of this some songs like "Cats in the Cradle" (Harry Chaplin) being all A sections with a bit of instrumental Interlude.
Stevie Wonder wrote some A only songs also and I think he's a brilliant songwriter. My conclusion is that the better the lyrics (story) the less music required (if you will). Folk Ballades are great examples.
From the 80s to 90s (I'm generalizing) pop songs became more: Verse / Chorus...which extends into Verse / Pre-Chorus / Bridge etc.
A good basic knowledge of popular song form is most likely fine for any commercial work.
A good book for popular song is by Jai Josef's and I think is called “Writing Music for Hit Songs”....perhaps a shallow title but good information. Again....not suggesting you get it.
Remember most all "form" comes down to unity-contrast. Sketch-sketch-sketch.
Let me add: I studied Art Song with Bryant McKernan. I wrote a number of them. Though I do not currently write Art Songs or many songs for that matter, learning the concept of prosody has served me well in arranging. In arranging accompaniment to a melody with lyrics the concept of the music telling, or supporting the story is very important just as in picture scoring.