I think it's a good idea to sketch out the novel, but not completely. Just have the beginning, middle and end. Then, write everyday, as much as you can. Setting yourself up to write a specific amount, like 1,000 words, might prove self-defeating. You might think, "wow, I couldn't make my thousand word limit today, I'm a loser. Ah, the heck with it." Instead, just write whatever you can. Don't keep a specific word count in mind, just pay attention to your story, flesh out the details and get to the end.
Once you're there, step away from it for about a week. Then, go back, read it very carefully, and have a legal pad next to your computer (or, if you've printed it off, next to your manuscript). As you read, make notations where you might be able to expand your writing. For example, in my book, I had someone attending a Halloween party as an adult. When I read it through, I thought, why not have him go to a Halloween party as a kid (there's an extensive flashback), then I can contrast the two! That resulted in a whole extra chapter of approximately 20 pages. Don't write anything until you've finished reading through your first draft and making the notations.
Once you're done, read the legal pad, make more notes, and list exactly where you can enlarge and improve. Then, start incorporating the changes into the original manuscript. I went from 250 pages to 400 pages doing that, all within the space of two months. I ended up doing it AGAIN, and ended up with 500 pages--a total of 92,000 words! That's what got my novel sold to Samhain!
Good luck!