For the "big" ideas that are what a book is about, I am inspired by something I learn that surprises me and causes an emotional reaction. For The Girl Who Wrote in Silk, it was the experiences of Chinese-Americans during the late 1800s when they were being violently expelled from communities all over the western U.S.
For daily inspiration to sit down and write, I make sure to put things in my book that I'm totally into and want to spend time with every day. For example, I absolutely adore the San Juan Islands so I had to set my book there. It was like taking a vacation every time I sat down to write. It's also little things, though, like the fact that I love tea. By having my characters drink tea, I feel like I'm living my passions, no matter how small, when I'm writing.
Beyond that, inspiration comes from seeing my page number growing. There's nothing more satisfying than getting nearer and nearer to the end!