Making Your Submission Better
1. Have two or three other writers you know, respect, and trust critique your work in-process. This doesn't have to be every chapter (though I know writers who find that helpful), but perhaps at 1/3 done, 1/2 done, and then after first-draft. Always take what they say with requisite grain of salt, but this should help you avoid any massive structural/narrative problems before they become unsolvable.
These need to be people who understand story, craft, and writing because they should be responding in part to the mechanics of the story. They don't need to love your genre--they just need to know how a novel goes together.
After you've completed that draft and are satisfied, you need to find readers.
2. I recommend a minimum of three different kinds of readers, though you can obviously have multiple readers of each type.
A.) Someone who loves you unconditionally. This is generally just for your morale, though if they hate the book, you might be in trouble.
B.) Someone who has liked your work in the past but isn't a great friend or a blood relative. This person is on your side. They'll go in optimistic. They're your "ideal" reader in some respects.
C.) Someone who has never read you before. They're the agnostic/skeptic you need to convince.
B. and C. should be well-read folks with opinions to share. It's best if they do like the genre you're writing in. You're basically just getting "market feedback." The sample size of opinion will be small, so again you need to take critique with a grain-of-salt but hopefully there will be feedback that helps you refine and tighten your novel.
At that point, your story will be better than it was at first-draft. Guaranteed.
Next time, we'll talk about the role (or lack of role) of editors in the life of your book.