You need an editor. I don’t care if you got straight A’s in high school English; every author needs an editor. I’m an editor, and guess what! When I write, I have editors! Even picture books require editors. Our eyes can trick us into believing we are seeing what we intended to type rather than what we actually typed. We need a trained set of eyes to spot what we can't see.
Just so you know, I’m not critical of people’s day-to-day writing. I don’t critique my friends’ Facebook statuses; it doesn’t bother me when a post contains typos or other errors. Facebook is for sharing thoughts and info informally among friends. But a BOOK, that’s different. The message can get lost in the unedited mess!
Good editing also costs money. “A laborer is worthy of her hire,” as the saying goes, as well as “You get what you pay for.” I once edited a book that had been “critiqued” (for free, of course) by the author’s writing group. The author was offended by all my markings, feeling that her writing group was as good as a professional editor, I suppose. They had complimented her, and here I was, pointing out inconsistencies and factually false information! But the reality was that I was doing the job I was paid to do, and doing it to the best of my ability, applying all my resources as well as plenty of time. Writing groups can be helpful, but their help cannot take the place of the work done by a good editor.
So please, if you are going to self-publish your book, don’t rush into it. Be willing to work with an editor and take things slowly, especially if you hope to make a career out of writing. Present your best work to the public, and you’ll avoid reviews that complain about technical mistakes in your writing. Not only that, but your message will stand a better chance of being clearly understood.
Disclaimer: I don’t tell you that you need an editor to get your business. My services aren’t advertised here or elsewhere, and that is because I stay pretty busy with one publishing house and word-of-mouth work, which is how I like it. I’m telling you that you need an editor because I want you to publish your BEST work!