Stephen King (along with most “How To Write” books) advises writing every day, and says you have to exercise your writing muscle. What does this mean?
Transients – To borrow a term from electrical engineering, you go through a transient phase to reach steady state. Steady state is where you want to be. (writing) Transients are what you do to get there.
If you don’t sit down to write regularly, you go through a longer transient. Your desk might be covered in junk mail. You might have trouble finding the Scrivener file of your novel if you’ve worked on other projects. You might need to remind yourself of details of the story itself: a minor character’s name, the color of the hero’s clothes, or whether an important conversation had already happened or not.
But if you write every day, you sit down at your desk and start writing. You remember where you left off, the necessary files are already open. You reach steady state almost right away.
Inhibition – You might feel a certain inhibition about diving in and starting to write if you don’t it all the time. If you’ve been away from it for a while, you may feel pressure to write as well as you remember writing in the past.
But if you write every day, you don’t feel inhibited. You know from experience that most writing starts out rough. And besides, the first thing attempt is not a horrible first draft, it’s a sketch. Artists produce lots of sketches before they produce the finished work, so do writers.
Your neutral point – If you’re writing all the time, you’re more likely to be thinking about the story when you’re not at your desk. If you’re thinking about it, you’re working on it.
There’s a book about doing research in which a scientist promoted to department head said, “I don’t have time to think anymore.” He meant that when he was a scientist, he thought about his research when he wasn’t thinking about anything else. As an administrator, he was trying to do research in his spare time, but it was no longer the neutral place his thoughts went to automatically. I’m usually thinking about writing when I’m not thinking about anything else, and I know that some of my best dialog, telling details, or metaphor comes to me when I’m away from my desk.
As a everyday writer, the last thing in the evening, I usually think about what I want to write the next morning. It’s not more of a plan than a few bullets about what needs to happen in a scene, or a vague idea about foreshadowing something, but it sets up the expectation that, first thing the next day, I’m going to sit down and write. I also get to ruminate on it overnight, which seems to be important.
Of all of these, I think the third one, the neutral point, is the most important. Writing takes a lot of time, and the more time you spend thinking about your story, the better it will be.