remember writing is hard work (code or prose)
Show respect for the person who created the copy. Remember that writing is hard work, and writers often feel sensitive or defensive about changes in their copy. Know the rules and conventions of language. You owe it to your writers to know your stuff. Don't move a comma or change a word as a matter of personal preference. Base your revisions on what you know to be correct, as supported by a standard reference guide. Distinguish between grammar and style. Be more definite when you recommend changes involving grammar and usage; be less definite when you recommend changes in idiom and style. Don't present your notion of style ("It's wrong to begin a sentence with and or but") as a rule of grammar. Don't over-edit. Remember, there's more than one right way to do something. If you tend to be overly zealous in your editing, first read the copy from beginning to end without making any changes. This approach will allow you to tune your ear to the writer's voice before you begin altering the copy.
Substitute few words and this advice fits for commenting on code, too. Good points to remember for pairing, technical reviews, and inspections.