When it comes to explanatory text, practical help ought to be a writer’s principal object. The point is to explain what it is and how can we achieve it. Regarding sublimity, I will do my best.
How to explain? The source of distinction of the greatest poets? Grandeur. It produces ecstasy, not persuasion. Persuasion we cannot control, but sublimity tears like wind.
Nothing is truly great that is great to despise: wealth, reputation, absolute power. The wise disdain these. What of literature depends on nature can only be learned through art. Some marks: it is impossible to resist and it endures, leaving a long impression.
Inspired emotion, a kind of madness and divine spirit, can help. Another way is to make the mind ever-pregnant with noble thoughts. Selection and organization are not to be underestimated. See Sappho here, how she layers. Consider imagery, Phantasia: the point being, to astonish. In this vein, consider hyperbation: the arrangement of words and thoughts outside the normal sequence.
Also, remember metaphors. Consider the bodily tabernacle, the head as citadel; the heart a knot of veins; spleen, a napkin for the insides; blood, the fodder of flesh; death, a loosing of the cables binding the soul’s ship.
Inspired by the first-century manuscript “On Sublimity,” widely (though not uncontroversially) attributed to Cassius Loginus, as translated by D.A. Russell. Finding it in my Norton Anthology of Theory and Criticism, I was heartened by the slightly bombastic and utterly romantic confidence of this writer, moved with urgency to explain the sublime.