I originally read practice in this context as exposure, the idea that if you just study a lot of literature you'll develop a taste for the good stuff (basically the dominant model of lit studies). But now I'm wondering if Hume saw practice as actually doing the art. Like, instead of just studying poetry, I actually went out and wrote some poetry. My taste, then, would develop through a combination of external and internal experience; it would be practice of both input and output.