It has been said that preparation is the key to success. I’ve found that’s true for writing as well. Preparation, of course, can mean many different things. Some writers like to come up with extremely detailed outlines while others merely want to have some vague idea of the setting and go from there.
The most important part of preparation, then, comes back to what you need as an author. Do you need a full, detailed outline of every event and character arc? Do you just need some quiet time before you sit down to write? Do you need snacks in your writing area so that you can focus on writing without interruption? Do you need to make sure other stuff (chores, work, whatever) is done first, so you don’t have to take care of it later? You have to have a good level of introspection, to know what you need to get to the task at hand.
Trust me, the simple things are the ones that can interrupt the flow of words. Writing is a purely mental exercise and if you have distractions or concerns about outside events, they can make it difficult or even impossible to write. The same goes for your writing itself. If a scene or plot device isn’t working, it might become a source of irritation or distraction that can impact the rest of your writing. Take care of the things you need to do before you start writing.
That said, procrastination is also a factor of preparation. I’ve wasted entire weeks and months before “getting things ready” for writing. That could be outlining, world-building, or figuring out the mechanics of what I’m working on. I’ve also seen authors who set aside a day to write who then think of all the other things they “should” be doing and end up doing those things instead. Not because they have to be done right then, but because they’re afraid to try and fail at writing.
Writing is hard. Set yourself up for success. I find the preparation I need to work on different projects changes from story to story. Some stories practically write themselves, with little or no preparation. Others require a great deal of time spent focusing, outlining, and getting myself into the mindset. Get to know your writing style, what kind of preparation you need, and take care of it. Lastly, don’t use preparation as an excuse to procrastinate. Getting words on the page is the goal and even if they aren’t the perfect words, they’re another step along the road to success.