I communicate with the author or writer to understand their writing style and goals. For creative writing, I'm willing to be lenient in the way the text and dialogue flow so that they are clear but still adhere to the author's specific style of writing and keep their characters consistent.
For research papers, articles, etc. I will check facts and recommend websites or publications that contain additional or more accurate information if I feel the document is lacking in depth or detail.
First and foremost I will always pick out incorrect grammar or spelling errors. I will replace words for clarity and precision, correct any misspellings, insert or omit necessary or unnecessary words, and rearrange parts of a sentence to make it more coherent.
I always inform clients of which revisions I've made, where, and why. I do not inform of spelling, punctuation, or capitalization changes. I make sure to save a copy of the client's original document for references to what I have changed. A second copy will contain notes of my changes. A third copy will be the final product.
If a client takes issue with any part of the third copy, I will undo any revisions made to that part and try again until the client happy with my service.