Some call it line editing, there are different names but this is where I get up close and personal to the writing. I identify clunky phrasing, clichés, wrong tenses, inconsistencies in voice, style, head-hops, exposition, filler and so on.
Using the Tracked Changes feature in Word I will correct obvious errors and mark or flag any issues.
While this is not a structural edit, I will comment if I find any structural issues or continuity issues with the plotting but my main focus is in the flow of language and correcting any mistakes.