Think of a child with a piece of play-dough, smashing it this way and that, playing with shapes.
Or a kid with watercolors, splattering paint on a paper to see if any patterns emerge.
Get everything out of you and onto the page, keeping always in mind that much of it might end up on the cutting room floor. Again, this is the what.
Once you’ve got the what, not comes the fun part.
Rewriting and revising.
You no longer have to worry about staring at a blank page. Here, whether you take three or four, or even fifteen to twenty drafts, is where you carefully craft the how.
What’s the best, most powerful way to form these sentences I’ve already written?
Again, this is your job. Do not send it to the editor until you’re sure you’ve done your utmost best.
If you are self-publishing, you’re going to need to work even harder to avoid errors which might alert the reader that your book is self-published. The last thing you want the reader to think is that you published your own work.
You want every reader to think your book has been professionally published by a major publisher. Otherwise, you risk the reader not taking your work seriously. When your book looks amateurish, most people won’t even bother to read it, much less review it or recommend it to someone. One careless mistake early on could prompt the reader to simply toss your book aside.