"Nobody knows anything."
In this wonderful book on writing, he says again and again, "Nobody knows anything," until it is a mantra that you will have imprinted, etched, and coded in your brain. What does it mean? For me when someone says, "You can't write a book over 300 pages and get it published." Or, "Nobody reads the quotes at the beginning of a chapter so don't put them in." Or, "The only way to write is by outlining." Or, "The most creative way to write is to write without any constraints and not knowing what will come next." Or, "You have to have an agent." Or, "Nobody is publishing coming-of-age stories anymore." Or, "Nobody will buy a book on quilting (move over How to Make an American Quilt book and movie)." There are many many more maxims of writing that will come across your path but, as William Goldman says, "Nobody knows anything." People guess at what will sell. They guess at what will break out and what will collapse and it's usually based on past experience. Never a bad thing unless you try to apply it to all cases in the future.
It's kind of like people who have been in drug treatment. (okay okay, just go with me here) When you ask them, "What kind of treatment would you recommend I go into (because, say, you need treatment)?" they tell you to go into the kind of treatment that worked for them. People who have been in AA say AA is the best. People who have been in a therapeutic community say 24-hour round-the-clock, keep-me-busy-all-the-time and do-group-to-death is the best. The problem is you are not them. I don't know what treatment will be best for someone unless I've done a complete and thorough assessment of their illness.
The same thing works for writing.
What will work for you?
Should you use an outline? If it helps then use it. If it doesn't then don't.
Should you get an agent first? It's usually a good idea but I know people who have published without one. Its harder but if you know people and have contacts...
If your book is over 300 pages and that's the right length for your book, then keep searching for a publisher until you find one that believes in your work. Is it possible you won't find one? Sure, but there's no even money bets on publishing. They're all long shots. You just keep the faith and keep entering the starting gate for the next race. Perseverance, faith, and support can pull you through.
I queried over 70 agents before I got my first one.
My novel is over 300 pages long.
And it was published.
Remember. "Nobody knows anything," unless it applies to you.