I particularly like this bit of wisdom:
Accordingly, it is well that we ourselves also, when elaborating anything which requires lofty expression and elevated concepetion, should shape some idea in our minds as to how perchance Homer would have said this very thing, or how it would have been raised to the sublime by Plato or Demosthenes or by the historian Thucydides. For those personages, presenting themselves to us and inflaming our ardour and as it were illumining our path, will carry our minds in a mysterious way to the high standards of sublimity which are imaged within us. (Chapter XIV, Part 1)
Longinus is saying that we can learn from the masters. While it is not necessary to stop and think how Homer might say it, the absorption gained from reading Homer, et al, will find its way to influence our patterns of speech and writing. You can see Faulkner’s influence on McCarthy, and McCarthy then takes it a step further in other directions. Anyone who has read and loved McCarthy cannot help but develop a feel for stark imagery in description.
In other words, read, read, read.