Moving a manuscript from good to sold takes a lot of axe sharpening.
Then, the real work begins.
Sharpen: if you don't have an agent or even if you do, consider paying for a critique from an industry expert who sells or publishes what you write. Find one through your SCBWI chapter, Kidlit College, Writer's Digest, Twitter kidlit contests, Kidlit411, Rate Your Story, Children's Book Insider/Write For Kids, etc. They are out there.
Sharpen further: try the suggested revision even if you don't think it will work and/or improve the manuscript. Copy the manuscript into a new file called, "It will never work" and just try it. Do NOT dig in your heels at this stage thinking you've already done enough work on this manuscript. The revision that moves the work to acquisition might be next! Transparency alert: this stage is my cryptonite. I certainly recognize the value and I do it, but I start out looking like Grumpy Cat's identical twin.
Sharpen even futher: read the manuscript to a new crop of target audience members. I'm not talking about your writer friends, your family, or your trusted beta readers. (What?! You aren't reading the manuscript to your target audience? Gong!) Notice where their sweet little eyes wander (ooops, need a revision there!) and where their happy little faces engage (huzzah!)
Sharpen even furtherest: compare your latest version to the published book(s) closest in feel, theme, style, etc. to what you want your published book to be. (What?!? You haven't looked for comp titles? Gong!) Really dissect that comp title. Type it out in pages, study it, tape yourself reading it aloud and listen to it. Where do you engage? Lose interest? Revise accordingly.
Is your axe as sharp as it can possibly be?
If so, your manuscript might be ready to submit. I wish you the best of success. Let me know when you get to acquisition.
Feel free to share other sharpening techniques, too.