I’ve been an editor for over five years now and I wish I’d done it earlier.
What I’ve learned:
Editing should be a partnership between an author and editor. The editor may have the upper hand when it comes to wielding the Sword of Grammar/Spelling/etc., but it never does to be pedantic. If there’s one thing that does my nut, it’s when an editor ignores the voice. A high-school dropout who’s grown up on a ranch in the wilds of Montana isn’t going to speak in a grammatically correct manner nor are they going to think like that. So, when editing a manuscript which has been written in close third or in first person, it’s best to pay attention to that voice and protect and encourage it rather than stamp on it with grammatical rules and “you can’t do that” comments.
I think it helps that I was/am an author. I can see both points of view.
I see a manuscript as a partially polished gemstone. It’s my job as an editor to work with an author to make sure that the gem is polished to perfection.
One of my favourite things is working with an author over time and seeing how their style develops and evolves. As an editor, I hope that I never stop learning and never stop developing and evolving.