School marms belong in second grade classrooms. In 1952.
Copywriting empowers you with much more flexibility to treat grammar and punctuation like putty in your hands.
This does not mean you can be lazy – nor ignorant of the rules. Like the proverbial Picasso who must master realism before unleashing his or her creativity, you must know the rules so you can innovate judiciously.
However, the main goal of copywriting is to communicate. In many cases you can think of it almost like spoken casual dialogue. Play with grammar and punctuation so that the reader reads it as you want it to sound.
Use commas or dashes to indicate pauses and rhythms. Start a sentence with “And”. Throw verbs to the wind and use a sentence that is just a phrase. Use three of them in a row. A full stop is more definitive than a comma – so if you want to emphasize each item in a list, make each item a sentence in its own right. (Compare “Lights. Camera. Action.” to “Lights, camera, action”.)
Time to Reiterate:
Picasso your grammar and punctuation for a good reason. Otherwise follow the official rules.
People can tell a cheap unskilled Picasso rip-off from a mile away, and the same is true of poorly written copy. Don’t go abstract because you can’t draw. Don’t scatter commas across the page like fallen eyelashes because you don’t know the proper rules for usage.