Here's what I do before writing / editing:
Research and compile and organize a ton of material from which to pull. I'm only realizing I do this as of today. My first draft is complete and I should be editing this very moment. But first I researched (videos, blogs, forums, opinions, etc.) and made a very structured list of how I will approach edits.
Grammar is the least of my concerns right now.
First will be more polished 3rd person POVs and I plan to include all four protagonists and the antagonist. I want each POV to be so unique that you know what character is doing the thinking / acting / talking without me telling you.
Second will be identifying unnecessary Adverbs and Adjectives and instead picking more effective nouns and verbs.
Third will be checking grammar... Among other things, this includes saying aloud each sentence of the entire book and if a sentence sounds awkward, fixing it. Also the structure of paragraphs... especially regarding dialogue.
Finally will be catch-all... Some chapters are 12 pages long... some are longer.. some are 2 pages. This in itself may not necessarily be a problem, but I would prefer some consistency.
After I've done this (and effectively gotten the book as far as I can get it) I will put it in the hands of no less than 2 (but preferably 3) alpha readers. (would they be beta readers at this point??) Then I will take into consideration what they say and go from there.
It's like Stephen King said, (and I paraphrase): Having only one test reader is useless. If one person's opinion is against a detail in my book, it's theirs vs. mine and obviously mine is more important. Therefore, have two or more and look for similarities in critiques.
That is all.
Time to stop procrastinating.
Feel free to ask why I chose that particular blog title.