If you're writing fiction, what's a reasonable daily output? It's the issue beyond all others--all the technique talk, the strategizing, the research, the preparation. At some point you have to begin your novel (or short story), and put black words on a white paper or monitor screen. We all know authors with reputations for high output: Stephen King, Joyce Carol Oates, Louis L'Amour (100 novels), Isaac Asimov (400 books). King recommends a minimum of 1500 words per day, six days a week, along with 4-6 hours of reading today–all well and good if writing and reading are the only things you have to do.
Other novelists are known for the slimmest of bodies of work–and some for a single book: Harper Lee, To Kill A Mockingbird; J. D. Salinger, Catcher in the Rye; Anna Sewall, Black Beauty; Boris Pasternak, Dr. Zhivago; Leonard Gardner, Fat City (my favorite first novel). I purposefully did not list Sylvia Plath, The Bell Jar, and John Kennedy Toole, Confederacy of Dunces, because both authors suffered from serious life issues that likely prevented a higher literary output. The authors at the top of this paragraph, however, lived long beyond their early works, but for whatever reasons did not write much more. One might forgive Harper Lee, whose novel would be hard to top; there is something to be said for stopping on a high point.
But this is about you. How many words/pages should you be writing on a day?
Let's start with the assumption that you have managed to carve out some writing time for yourself. You have most of a day to yourself. Or better, several days running–a five day week, let's say. If you're just starting your novel, your output will be smallish. But try to set a goal: by week's end I will have one good chapter, or 15-20 or so pages. That's only 3-4 pages, or on toward 1,200 words per day. Not a lot, but a start, and it's good, careful writing that you're pleased with. This latter point is no small matter; when starting, it's probably better to have a smaller output of quality pages than a stack of rushed work--unless, of course, you are Jack Kerouac.
When your novel is up and rolling, your output will increase--could easily double. You will be able to spend more and more hours at your desk. You'll have the urge to come back later in the day (assuming you start writing in the morning) for a second shift. You will be eager to get up the next morning and begin writing. At peak stride, you might write up to ten pages a day, or around 2500 words. Commercial and pulp fiction writers would laugh at these numbers, but I'm talking about serious, thoughtful, literary fiction. And in the end, finishing a full draft of your novel is about math. If you write three pages a day, 100 good days of writing will get you close to a book-length manuscript.
Final thought: if you're a perfectionist, your output is going to be half or possibly much less than the above numbers. In the end, of course, your literary output is all up to you. Are you a writer, or aren't you?