Great thread. Here are my thoughts on this as a writer.
Many people struggle with long-form writing, such as a book, because they haven't outlined things. As much as we all hated to do it in school, the outline is a powerful tool to keep things on track. Many feel it restricts their creativity. I disagree. An outline doesn't determine your style or your syntax. It's a guide. But, more importantly, an outline is a framework in which your creativity can roam around. In my experience, most people who object to an outline for long-form writing don't have a clear vision for what the final outcome is to be. Are there examples of people who write great books without an outline? Sure. But, for most people, we need an outline. It also helps you out of those times when your brain is processing other things in your life or other writing projects. If I'm inundated, I find an outline can allow me to shut out other things and return to a more clear mental place for that writing.
Secondly, and specific to an approach to dealing with writer's block, is the wonder of stream-of-conscious writing. My experience is that many people who attempt to write don't want to go through an iterative process of writing, writing again, rewriting again, and then rewriting yet again. I believe most people try to compose what they feel is a final product upon first draft. I feel that's crazy and often retards the writing process. Do you want to be 80% there on first draft? I think that would be an excellent goal that your first draft of a long-form piece is 80% of what the final form is with 20% of it in rewriting and editing. So, the self-applied pressure of thinking the writing needs to be put down in final form can cause a metal paralysis of a kind. Just get something down, as has been written already. One fun and intriguing exercise to get something flowing out of you is stream-of-conscious writing. For those who may not be familiar with this idea, it is simply stringing together words, phrases and sentences that may not even be syntactically accurate and often appear to be non-sequitur. Some would call it gibberish. Others call the output nonsensical. What you write may not be incorporated in your working text at all. But, you allow your brain to spew out thought streams and you simply take dictation. You're not thinking about if any of the thoughts are relevant to your text or even coherent or progress in any way. I use the metaphor "puking on the table" to describe this idea. You simply expel thoughts and your hand writes or types them out. This technique is enhanced if you are a fast typist. But the actual getting down of the stream of thought is the therapeutic part of it and has always worked for me to get past something that holds me back in writing. Besides, if you are writing fiction that contains character dialog, it is excellent practice because many of us actually speak this way and the technique helps us to write a bit more like we speak, which is good for believable dialog.
"Stream of Consciousness is a type of writing that originated with the works of psychologist William James (Brother of Novelist Emeritus Henry James). Basically, its purpose is to emulate the passage of thought through your mind without any inhibitors. For that reason, sentences become longer, less organized and more sporadic in style. Its lack of structure is not for everybody, but that doesn’t mean there isn’t any order. Stream of consciousness permits deeper patterns of order to emerge, ones based on the genuine movement of information in your brain. It also permits writers to simulate different forms of consciousness, such as dreams, comas, drug use and hallucinatory seances."
Here's a great article on stream-of-conscious writing: https://qwiklit.com/2014/03/22/10-writers-who-use-stream-of-consciousness-better-than-anybody-else/