Be reasonable in deciding if an edit should be made. Some errors are intentional. I try to avoid edits where the only edit is to correct one or two typo's.
I personally try make an edit if it will make the post clearer and easier to read, not on personal choice on how it should be formatted etc.
These are not rules. These are my personal editing preferences for when I make an edit myself. I try make edits that wouldn't annoy the OP. Be nice.
Add paragraph breaks to break up long walls of text. Make the actual question obvious. If it's a short question, this isn't strictly necessary. But I have been guilty of doing it (I then try at least incorporate several spelling and grammer corrections at the same time).
If a paragraph of criteria is a confusing jumble of criteria/rules and examples, sometimes with brackets within brackets etc, I consider adding bullet lists with the examples indented underneath the criteria/rules. Trying to keep the same sentence structure that the OP used.
Edits shouldn't change the spelling from American English to English English. Let the OP write color/colour as they choose. Obviously if there is a mix of spelling styles in the same question, then we can fix so that it is uniformly American/English all the way through.
Don't correct spelling mistakes and errors that are obviously intentional, unless it really detracts from the question. Eg puns.
If the post is only a few hours old and the OP clearly states they will edit later, either in the post or comments, and it's only a few errors, I try wait them out. Unless it is something really distracting like absolutely no paragraphs breaks or you need to make the question sentence really obvious :). They may have already noticed the typos/mistakes and they often will clear them up themselves when they add clarifications to focus the question. Especially if it's a typo that can be attributed to autocorrect. If they have already edited, and there are still errors, go for it.
When editing Headings, try stick with what the OP had written. I try leave headings alone as much as possible but occasionally a larger Heading edit is warranted.
If someone rolls back an edit, don't make the same edit suggestion again :)
If someone makes an edit on your post/answer that you don't agree with, simply rollback. They should understand. If the edited post does actually make the post easier to read in some way, rollback what you don't agree with and add any positive changes yourself.