Copy editing is all about helping craft someone's
writing to be more compelling to an indifferent reader.
(In other words, it's no different than writing an ad.)
Whether it's for an ad or an article the principles of editing are identical.
Advertising notwithstanding, writing is all about communicating ideas.
Editing is about making those ideas leave the most indelible impression possible on its intended audience.
Just like they do in an ad.
As a result editing involves knowing for whom you are writing, what their interests are, what their biases may be, and, most importantly, how to anticipate and address them.
But editing today is more than just understanding how to arrange words on the page more effectively.
It's also about knowing how to arrange the images that go along with them just as effectively. (It's important to know that all of us have a visual vocabulary of images just we have a verbal one, because images have definitions as much as words do. And when you combine them effectively the results are very powerful.)
You see, it's all about delivering whatever a message or article is, with the greatest impact.
In order to sway or influence a reader in a way that either solidifies a point of view or gets them to reconsider a previously held position by introducing information in a fresh, engagingly new way that has the effect of making them re-evaluate it.
With just the right amount of words (and images), laid out in an inviting format to make its case.