One issue that beginning copywriters often struggle with is realizing that good copy does not always need to follow the rules of grammar. Now there are always differing opinions on this issue, however the fact remains that effective copy often breaks the rules of grammar.
This is true because copy mirrors actual speech, and people do not always speak the way they write. In effective copy, we often see one-sentence paragraphs. We see sentences that omit the subject. Sentences sometimes begin with the word ‘AND’. The best copywriters will even frequently employ one-word sentences, or even one-word paragraphs.
Now when we point out these facts, it should not be assumed that copywriting can be sloppy. The exact opposite is true. Again, the best copywriters are careful with their grammar. They only break the rules for specific reasons, usually for emphasis. Copywriters at the top of their craft routinely study the standard works on writing, from Elements of Style by Strunk and White to On Writing by Stephen King. A good copywriter will pay attention to word selection, alliteration, and all the other elements associated with good writing. The very best copywriters read their copy out loud, usually several times, to ensure the smooth flow of words.
An appropriate comparison can be made to a professional athlete. Whether a baseball, football, or basketball player, the pro will often have his or her own style. Be that as it may, they first learned how to execute techniques by the book.
Ultimately, as a copywriter the only rule is whether the copy effectively generates the desired effect or not (leads or sales).