Mike Barrier has reprinted his, Bill Spicer's and Milt Gray's classic 1969 Funnyworld interview with Carl Stalling, the only published interview with the most influential cartoon music composer.
Stalling didn't have much of a background in composition and unlike Scott Bradley, he didn't aspire to write music that would stand on its own as music. A lot of his scores, when you hear them on their own, have their share of passages where nothing much is happening musically except a few chords or a chorus of a popular song; that's not a rap against them, just that this is not film music that can be separated from the film.
He was mostly concerned with technical challenges, which is what he mostly talks about in the interview: how to synchronize music to action, how to balance music with sound effects, how to find appropriate musical phrases to suggest physical actions. Synchronization was the essence of what he'd done as a silent-movie organist and what he did as a cartoon composer: he was always coming up with new and better ways to make the music fit the rhythm and actions of the picture, and while other cartoon composers wrote prettier or more complex music, no one ever wrote music that was as perfectly responsive to what was happening on the screen. And this helped to establish that music for a cartoon could truly enhance the humor, because the more the music mimicked the action, the funnier it was.
Also the choices of songs can make people laugh if they recognize how the reference matches the action ("The Lady in Red" for Little Red Riding Hood and so on). In a way all those musical references are the ancestors of today's common practice of reinforcing the action with appropriate popular songs. (And when I think of how many songs are on those soundtracks that Warners no longer owns, I sometimes wonder exactly how much it costs to clear all the music for a Looney Tunes DVD set.)
My favorite Stalling synchronization trick, which I don't think any other cartoon composer used on a regular basis (Bradley did it occasionally but only occasionally) is the "blink" effect, where he actually writes chords for a character's eyes blinking. Stalling -- and later Milt Franklyn, who used the same effect -- often did this after a big laugh line, where the director is holding for laughs and nothing is happening onscreen; needing some action to hit with the music, he goes for the blinking, because that's the only thing on the timing sheet. But it's a hilarious effect, even if it wasn't really meant to be heard (in theatres, these "blink" effects are usually drowned by audience laughter).