As writers we can talk about craft, sentence structure, word choice and even title choice. But to readers the most important question is, do I care about the main character? Do I care enough to invest time going on this journey with them?
If you can make the reader care about your character and want- no need- to read more, then you have a story that will sell. All the craft and editing can be fixed, but if no one cares for your main character all the good craft and solid writing in the world can't fix it.
How do you create characters people care about? Make them as real as possible. Give them hopes and dreams readers can identify with. Give them flaws and talents. Readers want to identify with the main character. They want to see the best of themselves in this person. They don't want to read about someone who seems to stupidly walk into conflict. They want someone who is doing their best and still running into problems. They, also, don't want to read about someone so perfect that they can't ever be in their shoes.
Authenticity is important-but not so important that today's readers can't identify with the character. For example: if you wrote a truly authentic sixteenth century story, most readers would struggle with language and social/cultural differences. So you have to find commonalities between a sixteenth century lord and today's readers. How do you do that? I'm certain that people in the sixteenth century cared as much for their family and friends as we do. They gossiped. They worried about budgets and who left the candles burning in an empty room. They worried about who is stabbing them in the back and how they could be successful, and where they have failed. It is the sameness in those worries that draws the reader in and the differences that keeps the reader wanting more.
If your main character is a homicide detective give him strengths, ie. the ability to break cases and then weaknesses. Perhaps he can't communicate well with others. Or he has a sick mother he cares for, or his friends hound him because he doesn't always remember to change his clothes. Think about iconic characters such as Colombo or Monk- it is their little oddities that make them three dimensional and attractive to readers.
So, improving your odds of getting published boils down to a few things: knowing your readership; surprising them while meeting their expectations; giving them characters that are three dimensional and authentic. Good luck!