This is maybe more about being an artist in general, than specifically about writing, but I think intentionally trying to live an interesting life is very important.

Dave Chappelle talks about how the most valuable thing an artist has is their memories. You gotta go out and make some. It doesn't matter so much if they are yours or others, but what it does is it makes your work more human and grounded in human experience. Even if you write sci-fi or fantasy, it should be informed by your experience of what it means to be alive in this world.

I reached the stage of a (non-fiction) writing project where I had tons of notes, but no sense of what an eventual manuscript might look like. I discovered Zettelkasten and it was a revelation, not because I think it's the only way to write, but because it was an answer to my precise problem of how to turn a ton of notes into a manuscript. I'm still a long way from being finished with my project, but I can get my pen moving every day and that in itself has been an enormous relief.

To be consistent, sit down and write something, anything, every single day.

Even on the days you don't want to. Hell, especially on the days you don't want to.

Do it for long enough and you'll have written your novel, screenplay or story.

Now this isn't an advice, but I'm gonna share it anyway.

One of my family members knew that I wrote a lot of stories and poems and told me to stop wasting time writing them.

And when I think about it this way, I stop overthinking my stories and poems because at the end of the day, nobody is reading them except me.

I never received this advice, but I feel like it would've helped me get into writing well before I actually did. It's okay not to finish. The 50 google docs you have all show your work, how you're advancing your skills and expressing yourself more and more in each response. I used to only be able to write a few sentences before quitting, but now I go much longer.

Also, length doesn't matter. I used to constantly try to set goals for how much I'd write in far too short a period. This may be useful for some people, but for me I just got distracted, obsessed with reaching my unachievable goal, and it was far less then helpful.

I don't recall the specific wording, but the best piece of advice for me was something like this:

Don't try to be a writer. Don't try to be an author. Just write.

Having an ideal identity which I was constantly and very unfairly measuring myself against prevented me from writing anything at all because before I even got started I knew it wasn't going to be to the standards of my imaginary avatar. I now allow myself to write a mess because in that mess is some quality stuff which I can extract and expand on, and writing the mess is a lot of fun. I'm currently totally free of an audience I have to conform to, so my writing is totally free from any kind of restrictions other than what I prefer at the moment.

Similar to the OP (and other comments), the one thing I like to remember was a tumblr post from way back that boiled down to "write shit." It doesn't have to be good the first (or even third) time around. Allow yourself to write garbage. Look back at your drafts and half-baked stories sometime, see how far you've come. Work with the parts you like, acknowledge the mistakes and most of all, be able to laugh at the shit you've written. Can't get any writing done if you set unreasonable standards for yourself.

Kind of a numbers game, isn't it? On top of that there's the difference between your own taste and whatever taste a potential audience has

Luckily I only write for me; if it was for anyone else I would have stopped!

I am actually just writing an essay on this, I'm gonna nonchalantly past a couple of paragraphs relevant to the question.

Would it be proper advice if it wasn't the always present: "Just start"?

It's one of those simple but hard-to-follow rules that almost every aspect of everyday life things we try to get better at has. Just start is such a good piece of advice, because once you have written something down, you give yourself different reference points to think about under the shower, on the run, or at the store, and all of a sudden you come up with something new that further enriches your text. Its a collection of ideas that come at you randomly. The more often you think about a certain problem you want to write about, the deper you will go. Repeat this over a couple of iterations and you get a well-written collection of words.

What it also gives you is the space to think about these words, to think about the flow, narration, and intention. For the longest time I had a misperception that when you sit down to do something, it has to be done straight away. Some people are just such masterminds that they have a constant flow of good ideas. But then I heard someone famous say that "here's a song that I worked on for a couple of months" and all of a sudden it made sense, that writing is a process, a chain of iterations.

This first iteration usually won't be good because each paragraph is still an isolated piece on its own. Imagine the writing as being a color painting. The paragraphs don't yet have a common color board, each is its own flavor and next to each other they don't yet taste good. There is no color overflow from one idea to the next one. But when you reread it in a day or two, you can feel the flow of words without having to think too much about it. You are able to see different paragraphs carrying the same idea that can in different order have a much better sound or narration.

Don't be afraid of bad writing because it is inevitable. But have a process that will improve it as the iterations happen. What I'm looking for when I am creating something is the unique aspect of my idea, something that makes the piece original & interesting. How to turn something boring, that has been said a million times into something interesting. It can be playfulness between sentences, the interlinking between seemingly different paragraphs, or a small ongoing joke through the text that makes it relatable.

Even this pasting over for this comment made the draft of the essay now completely different. I see the unnecessary sentences, and as I had to rephrase a couple of sentences, I see what narration might look better. Hope it makes sense!

For me it was something along the lines of "you can't edit a blank page". And I know, it's a meme, but "just write, edit later". I used to get lost in planning and world building and then I discovered that I'm more of a pantser than a planner and voilá, here I am, actually finishing stuff.

Also, I came to like editing and revising now. I used to dislike it but now I enjoy it!