The number one thing that I attribute my growth as a writer to is keeping a daily journal. If you read my pep talk post, you know that I'm a big believer in the idea that a writer writes. Some days it can be really hard to find the energy to work on my writing projects, but I work to make sure that I write three pages in my journal every day. Three pages a day is the advice that I got from my mentor, Jennifer Sinor, and the advice Julia Cameron shares in The Artist's Way). Three pages takes me about thirty minutes every morning, although that length of time can vary depending on the size of the journal I'm writing in, and whether or not the pages are lined (I have small handwriting, so if the pages aren't line, I get a little out of control). At this point, I am certain that the number of pages (three) is really a matter of superstition on my part, but I believe it's important to spend sometime in meditative writing every morning.
I love journaling, because it's the most low-stakes writing you can ever do. No one is going to read your journals (if they do, get rid of those people (not like, kill them, but get them out of your life)), so no one needs to know that you can't spell the word 'unconscious' without spell check, and no one needs to know that you mix up effect and affect. You're allowed to throw away stress about grammar (which as an introductory college English instructor, grammar rules are surprisingly one of the biggest factors on a lot of writers' sense of writer's block) and write what you want to write.
At the beginning of the pandemic, when my mental health was a mess (it still is, but a more manageable mess), I spent every morning writing a list of ten things I felt grateful for that morning. I'd write a paragraph for each thing, describing the thing that brought me joy, and how it came to be a part of my life, and the joy it brought to my life. I should probably still do that, because it was a powerful way to start every day.
Since I stopped doing that, now I spend my journal either composing or transcribing a favorite poem into my journal, and follow that up with ideas for what I want to work on that day. I write about my novels and explore the sticky plot points, or confusing character discrepancies. I write about the relationships in my life, and explore solutions for potential difficulties that might exist in those relationships. I write about the books I'm reading (I spent a good part of last week and this morning writing about my dislike of C. S. Lewis's Chronicles of Narnia series). The thing about keeping a journal is that it's up to you how you use your journal.
While I stand by the fact that it is up to you how you use a journal, I do think that any writer should work to keep a daily journal. The most powerful thing about a journal for me is that it helps me do some throat-clearing before I sit down to write one of my major projects. I'm able to get out all my frustrations, or all of my plans, or whatever worries I have about the project, and then I can sit down with the actual writing project I want to work on, and just work on it. It's powerful work, and I think every writer should have a journal.