Many writers set a goal of working on their project for a certain amount of time per day. The danger is that it can be easy to rationalize that spending that time researching your topic on the internet counts, even though you end up spending "a few minutes" checking your email, reading the news, or updating your Facebook account.
In that case, you might say, why not set a word goal: a certain number of pages to be written per day or per week?
Well, that's better but maybe not quite good enough. In an interview in The Writer magazine, prolific novelist Peter Abrahams came up with a better solution:
"My goal is to put in about a thousand words a day and to advance the story."
He explains: "Those are two separate goals because you could write 1000 words a day without really getting anywhere."
In other words, if you write a thousand words describing the protagonist's house but nothing has moved forward in the story, it would be a good idea either to keep writing more or (preferably) figuring out what you can combine with that description that will advance the story.
Usually this change affects one or more of your main characters. Sometimes their situation is just different, but normally it is either better or worse relative to what they want it to be.
I think it's good not to get obsessed with this in your first draft, otherwise you may find yourself rewriting too much rather than forging ahead. However, it's an excellent method for assessing your first draft and figuring out what you would like to change in your second.
Abrahams and I are both talking about mainstream novels, not experimental ones; in the latter, anything goes. In the former, readers want the story to keep moving.
(For more tips on writing your project from the idea all the way through to the finished version, see my book, Your Writing Coach. It's published by Nicholas Brealey and is avaiable from Amazon or your other favorite bookseller.)