By choosing fellow writers, especially close friends, as your first beta readers, the readers lean more towards giving grammar and punctuation advice, as well as giving truthful- but kind- advice. Take T.C. Arc and I for example- we send each other our writing all the time because we know that the other person won't totally down grade our writing. There have been times in the past where I might send part of my work to a friend who doesn't write, and I'll end up getting a bit frustrated, because they don't know how to comment on a story without being seriously offensive.
After you have your first initial readers, send out your novel to a larger group. By then you should be more used to people reading your writing, and by sending it out to more people, you get more feedback on if your story is something a lot of people will like. Also, more pairs of eyes make it easier to spot plot holes and the like.
Now this last part can get veryyyy pricey, so I recommend using this site called Fiverr.
https://www.fiverr.com/?source=top_nav
Fiverr has so many editors and so much more for your book, all for more affordable prices than most places. I recommend using at least two professional editors, just because there are multiple different kinds of editors, and having more than one editor will ensure that your book has very few to no mistakes.