I've written on and off all my life, but I got serious about writing about four and a half years ago. And by serious I mean I wanted to learn as much about the craft as I possibly could, and made sure to write consistently - if not on a daily basis, then at least on a weekly basis.
I have to admit that at first I was obsessed with word count, including the number of words I generated every time I sat down to write. I kept a word log in which I'd tally how many words I wrote each day, and my goal was at least 800 words, five days a week (so about 4,000 words a week).
Four and a half years later, I have an entirely different approach. I still log my words, just because it's kind of fun and makes me feel like I'm being productive. But in reality I have switched to logging time instead. Because there's so much more to writing than just the words you generate. There's doing research for settings/characters, creating and filling out character sketches, building and fleshing out worlds in separate documents (OK, those last two deal with generating words, but they're a bit different, because a lot of that time is spent brainstorming and the words aren't part of the "official" manuscript), tedious revision (in which you return a tiring amount of times to the words you've already generated and decide to hack them out of existence or add on a whole bunch of new ones), polishing, I could go on.
Point is, I think it's a mistake to calculate your progress in terms of fresh words you write. I used to get frustrated when I didn't meet those 800 words and sometimes I'd even bypass necessary research or something else my manuscript needed at the moment just to squeak them in so I'd meet the quota. But, really, I was fooling myself and causing myself undeserved mental harm (not very severe mental harm, mind you, but you know what I mean). So now I go by time. Two-to-three hours of solid work on my story each day for five days a week, no matter what it needs at the given moment, will bring me ever so much closer to the completed/polished book it needs to be.