The analogy I go to is that of a living versus a dead language, which I got from my dad. He was a professional cellist for years before he said screw it, got an MBA, and went into finance, and I always thought this was some tragic compromise on his part—but when I finally asked him about it (well into my twenties and figuring out my own career) he said it was nothing of the sort: finance back then (~late eighties, trading latin american sovereign debt) had much more innovation, competition, and energy around it then classical music had (or will ever have again: it was dead). We should treasure the art movements we have while we have them.
(proceeds to rewatch several Xiao Xiaos)
(proceeds to generate dog photos with Stable Diffusion)
(proceeds to futz with midis, slouching towards counterpoint)
I mean: if you're looking to go straight to theory, the classic textbook is Johann Joseph Fux's, from 300 years ago. But if you're familiar with writing melodies (with some voice leading) over chord blocks, try eliminating the chords and composing a second melodic line. This line should imply the original harmonies, while maintaining a unique rhythm and contour—and you can then add more melodies as needed. Many theory rules, such as avoiding parallel 5ths or 4ths, are essentially design patterns ensuring melody distinctiveness.
Of course, it also helps to listen to a shit-ton of counterpoint (the right suggestion here is "Bach", but personally it was Brad Mehldau's music that got me interested in this).
The analogy I go to is that of a living versus a dead language, which I got from my dad. He was a professional cellist for years before he said screw it, got an MBA, and went into finance, and I always thought this was some tragic compromise on his part—but when I finally asked him about it (well into my twenties and figuring out my own career) he said it was nothing of the sort: finance back then (~late eighties, trading latin american sovereign debt) had much more innovation, competition, and energy around it then classical music had (or will ever have again: it was dead). We should treasure the art movements we have while we have them.
(proceeds to rewatch several Xiao Xiaos)
(proceeds to generate dog photos with Stable Diffusion)
(proceeds to futz with midis, slouching towards counterpoint)