The absolute, most important thing to getting a book published by a traditional publisher is perseverance and belief in yourself and of course, your book.
As you know, it took me 9 years of perseverance. Also a lot of head slapping (my own head, that is), eye rolling and groaning on my part.
If you are just beginning the process, or if you are years into the process, remember to do your research.
One of the most invaluable tools that I resort to is the book "Children's Writers Book Markets", which is produced every years. The updates in this book, as to which publishers are accepting, what they are accepting, send query or send the pdf for review, similtanious submissions or exclusive submission, the list goes one, will become your best buddy to get to know the publishing industry.
But one thing that stays the same, the publisher guidelines you must follow.
See, as an author, you have no rules. Publishers have all the rules. And if you want to get anywhere, you must follow their rules. This is just the nature of the game.
To just read the "Children's Writers Book Market" is still not enough. You must visit the publishers web-site, see what kind of books that have been published and decide if yours would fit in. If it does, write them a query letter with a synopsis of you book. Send a SASE (self address stamped envelope) for their reply. And, if they ask to see the book and want an exclusive submission, don't sent the book elsewhere. Then wait 6 - 8 months for a reply.
In the meantime, don't sit idle. More research, more queries. Query letters to other publishers can still be sent, even if a different publisher is reviewing your book on a exclusive submission.
Make a list of possible publisher to send our queries to. Make a list of publishers that accept manuscripts without a query and what kind of submission that publisher wants.
But make the list and keep track of where your manuscript is. This all becomes very confusing in no time. You need to keep a log of what was sent, where, and to whom.
I know. It's a lot of rules.
For all of the 9 years that I was trying to find a publisher, my manuscript was constantly somewhere. I received 30 rejections for this book. Talk about perseverance.
A published author also has to have thick skin. Rejections are not about you as a writer, rejections are about the immense choice a publisher has in manuscripts sent in that year. Some publishers receive upward of 10,000 manuscripts for review in a single year.
So, back to the research. Did I want to send my manuscript to a publisher that receives that many submissions? I usually tried to stay away from these large publishing houses. Being a first time author, I knew my chances would be less with these large publishing houses. I submitted to publishers that had a record for publishing the majority of their books with new authors. These facts are all in "Children's Writers Book Market".
So, just when I thought I knew what I was doing.
My first contract (which was forfeited by the publisher due to their funding problem) was with a small press that did 70% of their yearly books by new authors. Alas, I did get a contract, but it didn't work out. My second acceptance and contract was with a large publishing house that only accept 10% of manuscripts submitted for publication. This publisher received upwards of 10,000 manuscripts per year.
So after all of the years of my submissions to small publishers, I finally got accepted by a large publisher.
My advice--send your queries and/or manuscript to every publisher, big or small, as long as your book meets with their guidelines.
An interesting fact: Dr. Seuss received 27 rejections for his book entitled "Mulberry Street:" before it got accepted for publication.
This fact is a reality with many authors. Patients, perseverance, and a lot of head slapping (your own head, of course).
By the time you have a dent in your head, you will probably get accepted.