Don’t think about how it sounds, or how many passive verbs you’re using, or if you’re repeating the same word three times in the same paragraph, just make sure you get that story down before it leaves your head. Quality comes later, when you’re filling in the gaps, restructuring sentences, revising your work. It comes the next day, or the next week, after you’ve had time to step away from your work, forget about it, and then come back to read it with fresh eyes.
But when you’re writing that first draft, don’t worry about rules or perfectionism or, God forbid, what other people are going to think when they read what you’ve written. You have a story unfolding in your mind, so you better capture it, pin it down on paper before it escapes. Then you can remold. (Excuse the mixed metaphor.)
As Anne Lamott says in her book bird by bird, “Perfectionism is the voice of the oppressor, the enemy of the people. It will keep you cramped and insane your whole life, and it is the main obstacle between you and a shitty first draft.”
If you don’t already have a story up your sleeve, but you know you want to be a writer and you know you have to write a certain amount each day to keep your fingers/brain well practiced, then still, just write.
Pick anything to write about. Swings, a childhood memory, what your first thought was when you woke up this morning. And if you’re still hitting a wall, then numbly type what you did today or what you dreamt last night. I’m sure a story will pop out somewhere, after you get your creative juices flowing. Your mind will take a turn down different tangents until you’re writing about something you didn’t even realize was inside your imagination.
And like I said, don’t worry about your quality just yet. Don’t revise each sentence or word as you’re writing them.
It’s called a “rough draft” for a reason.