Don't be afraid to reward yourself once you've accomplished a goal.
Break your larger goal up into smaller pieces, then celebrate those milestones.
Finish a chapter?
Surpass the 100-page (or 200 or 500 or 1,000) mark?
Surpass 25,000 words?
Great! Then it's time to celebrate!
It doesn't have to be a big thing, like a street parade or taking a week-long cruise. Reward yourself with a little treat, like an hour playing a video game or watching a movie or heading out to your favorite restaurant.