Why? Because you can’t truly tell your story to the best of your ability unless you do. If it takes you fifty words to say something that only needs twenty, you don’t really know your craft. Those extra thirty words are unwieldy, clunky, awkward. Think of watching two dancers. One stumbles across the stage, trying to do the steps while the other glides gracefully, drawing your eye. That’s the one who knows their craft. Nothing against the one who’s struggling, but if you want to publish, you want your reader’s eye to be drawn from one sentence to the next.
How do you learn your craft? You keep writing. Revising. Reading. Practicing. Getting feedback. Acting on that feedback. Learning.
For example, if you get a note about a grammatical rule, try to make sure you follow that rule in your writing from then on. Don’t keep making the same mistake in your revisions and then in your next book and your next book.
If you’re doing some of your own research using one of the many writing resources available (and if you are, kudos!), put what you learn into practice in your writing. Maybe you’re learning how to build an effective story arc, or to flesh out your characters more effectively, or how to write more believable dialogue. Whatever it is, put it into practice! Don’t just read about it and then set it aside. Write practice scenes using what you’ve learned. Not every word you write has to go into a story.
Don’t be afraid to write down background information. J. K. Rowling wrote reams of information on every character in the Harry Potter series, even some characters that eventually got cut. She knew everything about even the most minor, including their birthdays, their family histories, their likes and dislikes, and so on. This is why her world was so believable to so many readers. She knew it inside and out. Do you always have to do this? Probably not. Will it improve your stories and characterizations? Hell yes!
Some writers seem to be most proud at how quickly they can churn out a novel, and I guess I’d be pretty proud if I could write 50,000+ words in a month or less. But how fleshed out is it? Do the characters seem real? Do you sympathize with them? Do you feel like the world they live in is real? Are you ready to step into it? Is the dialogue tight and well-written? Is the plot plausible and well thought out? Is the story enjoyable? Does it make your heart beat faster? Does it make you want to turn the page and find out what happens next? Are the details clear or muddled? Does the timeline make sense? If you know your craft, you could probably churn out a decent first draft in a short amount of time. If you don’t, you’ve got a lot of work to do, and you’re fooling yourself if you think you don’t.
Personally, I don’t care if it took you a month or three years to write your first draft. What I care about is how you apply your craft to the writing. When it gets to my desk, I’ll know if you know your craft or not.