One of the fundamentals of this, IMHO, is vocal meter, and it's a fundamental part of poetry. Songwriters should probably first and foremost be poets is some form.

I think it's actually quite helpful to conscientiously think about poetic meters for songs and lyrics. On of the things I find a little disappointing is where the meter is mangled to make the chosen words fit, rather than spending more time finding a words form that both says what one wants and has the appropriate meter. Meter is remarkably powerful, I think.

IIRC someone posted a link to one of the following a while back, but maybe this is a good time to link again.
12-tone -- A Brief Discussion Of Poetic Meter
12-tone -- Shakespeare's Favorite Poems


FWIW, it took me a little while, but I have learned to like at least some Rap, though usually where it has a jazz-fusion aspect.

Jazz relative beginner, starting at a much older age than was helpful.
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