You gotta have 'em.
Maybe it's three pages a day. Maybe it's 500 words. You have to have some sort of target, especially if you're writing something on spec, and there's no editor pressing you to hit a deadline. You have to hold yourself accountable, or you won't make progress.
At a writing conference, I recently heard a successful, published author express the view that page targets didn't work for him, that what worked for him was committing to write for a certain amount of time each day. If that's your approach, fine, but you can't spend any of that time faffing about on the Internet or playing Minesweeper, or you've shot yourself in the foot.
What do you do if you don't hit your target? Just like with any other failure in life, you resolve to do better the next day and you keep going.
At my recent retreat, my daily target was 30 pages (two chapters). On six of the nine days, I hit the target. Twice, I wrote only 15 pages (one chapter). On one day, I wrote nothing, because my fellow retreater and I spent the entire day talking through our respective plots and backstory, resolving some thorny issues and making important progress that way.
Usually, my target is fewer than 30 pages per day. Depending on the book, it's 10-12 pages, though with some projects, where the voice is particularly difficult for me, it's been as few as five. As I finish the rough draft of Project Alpha, my daily target is 15. As always, that's with 1" margins and writing in 12-point Times New Roman.
What's your daily writing target?