This isn't personal. Empirically, there are certain things everyone must do to get their manuscripts to the point where they don't suck. Hint: it's not a short or easy process, otherwise everyone would have a best-selling novel out there. Truth.
Now that we have that out of the way, check this list to see if your MS is where it needs to be:
Are you in a critique group? This one's critical. Yes, Mom and Aunt Sally are great cheerleaders, but they're not typically great at providing honest, unbiased opinions of your work (unless they're authors themselves, and even then you need someone who's not family).
Have outlined your story? This doesn't have to be done first if you're the type of writer whose creativity is stifled by outlines. But you MUST do it at some point.
If you're a first-time author, have you been working on your novel for at least a year? Yes, there are exceptions to this rule. Colleen Hoover wrote her first novel in a month. Which is so rare that she's the only person whose done this out of God-only-knows how many authors. Changes are, you're the rule, not the exception. If you're a debut author and haven't been plugging away at your MS while implementing useful feedback, it's likely not commercial-ready.
Is your grammar solid? You can have the best story in the world, but if your grammar is poor, most readers aren't going to stick around to find out. Yes, Fifty Shades of Grey didn't have the all-time best grammar. But back to my prior point: this is a one in a billion case. Don't base essential career decisions on statistical improbabilities. You don't rely on the lottery to pay your mortgage (or at least I hope you don't), so don't do this either.
Have you worked with someone who knows their stuff about building compelling story arcs and characters? Admittedly, I have an ulterior motive for putting this one on the list. But it is true. So if you don't pick me, pick SOMEONE. Everyone needs quality input on how their stories flow and how their characters come across from someone who's not inside their heads. SHAMELESS PLUG: I'm really good at helping authors with this! See my testimonials.
A nice-to-have, but not a must:
Have you had at least a chapter or two looked at by a couple of editors or agents that rep your genre? If you have, did you implement most of their advice? Here's the deal: agents and editors are in the book-selling trenches everyday. Their insights are invaluable toward helping you understand what sells and what doesn't. Get in front of some of these people, then listen to them. (Well, most of them. There are a few stinkers in the bunch, such is life. That's why it's important to get the opinion of more than one.)