The obvious, a closer look, and some personal opinions for good measure: this is what I've learned about copyediting at its most basic.
The saying goes something like, "behind every good writer is a good editor." I would argue this is true, because like it or not, the effect of a good piece of writing can be dulled at the hand of a typo or lapse in grammar judgement. This is where copyeditors come in. In short, copyediting involves everything from checking grammar, syntax, and punctuation correctness, to restructuring sentences to create better flow and clarity, and the tasks can even extend to fact checking and overseeing projects.
Editors achieve the same effect on writing as a glossy finishing layer on an oil painting: sealing the deal and delivering the final product. I would say the meain goals for every copy editor are these:
Master or seriously center these aspects in your copywriting endeavors, and you're well on your way to being a better copyeditor.
This is perhaps the hallmark of copyediting rules, since the purpose of the job is to refine and strengthen, not hinder. Sometimes, the most well-intending writers end up mangling a sentence if, for example, English isn't their first language or they are trying to describe something with complex technical verbiage in a paragraph flow.
You'll likely rearrange some things, but when doing this, make sure to replace the subject and verb in the way the authors intend and the way that makes sense. Sometimes the meaning of a whole sentence is unclear to begin with. When this happens in my case, I do my best to infer the author's meaning, rearrange it to be legible, and then leave a note calling their attention.
Ah, house rules. These can sometimes be the most difficult to keep in mind throughout an edit. They are like a software that you have to install in the base of your understanding of editing, to be removed and revised at the leisure of your editing overlords and then reinstalled, likely with some difficulty if you're like me and you have a bad memory, and this isn't your only job. That being said, these are just a given if you're working in most settings and should be given a great deal of effort.
Word has a helpful mechanism for showing fragments that could be more concisely worded. However, for a job like mine, where the copyediting comprises doing the minimal amount in order to make a text "print ready," it is actually my job to not change a clunky piece of a sentence, even if I don't personally like to read it.
The excersize of not slipping into a reader mindset and remaining unbiased is generally a good editing skill to hold. Afterall, the better you can help the writer succeed through your job, the better the fruits of your labor.
It may seem simple, but if something like an Oxford comma is discluded from half of a text, this can change how the eye scans the sentence. Once consistency is introduced, it's easy to notice a breakage. This is why copyeditors must be solid in their editing choices.
If an author has capitalized a specific term in some parts but not others, used Word's find feature to search the text for these instances, gather the term's meaning, and decide on which side of consistency you will stay.
If you own a cat or work from home, you understand what can go down at a desk that should be silent, organized, and ready for work. I once left a manuscript on an open laptop long enough for about 50 "f's" and a couple spaces to be typed by my cat, and depending on your level of awareness, more minor introductions like this could go unnoticed.
Similarly, errors in understanding a text can cause an editor to alter the meaning of a word or phrase, especially when dealing with unfamiliar subjects. Before changing a hyphen to an en dash, or adding a comma to what seems like a too-long string of scientific adjectives (such as ), run to Google Scholar, search through a page of google results to see how others have specified the name, or, if you're stumped, consult another editor or the author if you have access; and always ALWAYS, check back a bit in the text if you've stepped away from an open keyboard with live text.
Perhaps you didn't expect this at the end of the list, but I can say that the heart does get jolted for a second if you're asked to provide a random file from a few months ago that someone on the publishing end needs, but can't seem to find it. Always keep copies of your work and save things in their proper file format. Make sure your manuscript file names reflect the name of the project you're submitting, if you end up working with files in the same naming system.
A the end of the day, your job as a copywriter is to polish up the work of an author and other editors before you. Zip up any inconsistencies, infuse the piece with good grammar, unwind confusing sentences, and above all, ensure the intended meaning of the piece rings through. Harness these skills together, and you're at the threshold of a sharp-eyed, ethically-grounded editor.
Sources:
What Copyeditors Do, Chapter 1, University of California Press
What Does a Copy Editor Do?, LinkedIn
The Different Types of Copyediting, Archway Publishing