My son is writing a novel for a school assignment. I’m walking him through the process. Sometimes he gets stuck and doesn’t know what details to add and which to leave out. I remind him that he’s writing the first draft; it doesn’t have to be perfect, it needs only to be written.
I tell my writing friends the same thing; it’s the philosophy I live by.
I compare the first draft to a skeleton. The flesh and muscles along with the finer details (hair, eyes, freckles) are added later in future edits and revisions.
Often when I write, I add details, but if I’m stuck, I don’t spend time thinking them up if they don’t come on cue. I write on.
Here’s an example of what I might do if I’m stumped on a scene. The key in this passage is to get the character out of her home and on the way to work. Instead of spending unproductive time working out the details—or worse: being stalled in this one spot and not moving forward—I list what will happen and keep going with the story.