Rhetoric is a dying art: no longer seen in letters and literature but now reserved for politicians' lies; no more found in lovers' proposals, but all too frequently plastered across our eyeballs by marketers' banner ads and video campaigns; not now inked into parchment by poets' fountain pens, but only rationed to us in the short phrases found on the tombstones of the dead.
And yet, it isn't difficult: some subtle alliteration, a smattering of repetition -- repetition to reinforce but not to bore; an understanding of rhythm, of emphasis, of flow, of the music of words.
Write and rewrite, listening to each word, each phrase, ensuring it sounds as you wish it to sound, that it flows exactly as it ought to flow, that pauses and punctuation assist and do not impede your prose as it penetrates your reader's mind.
Rhetoric is also a science: it can be studied, practiced, and perhaps perfected. But it is in essence an art. It can be imitated, or even created, without being fully understood. You can memorize the definitions for Zeugma, Merism and Polyptoton, and precisely apply them wherever you calculate to be most appropriate, but this is not necessary nor preferred. If you write and edit until your page sparks and swims and floats and flares you will find these rhetoric devices appearing, seemingly by accident rather than design.
But beware, for rhetoric is powerful. It can make people happy, it can make them confused. It can change their ideas and beliefs, alter their characters, modify their lives in irrevocable ways. You should not practice rhetoric without flirting with ethics because people's minds are more easily swayed through language than through scientific fact, and it can be difficult not to use persuasive ability for personal gain.
Viva language. Viva rhetoric. Viva.