Trouble with keeping writing

Hi, I'm new at NaNoWriMo. I joined because my journalism teacher, at my highschool, told my class that if we joined and wrote a novel with NaNoWriMo, we could get extra credit. Well, I've been wanting to write a book for a while now, and have several ideas, but have trouble with keeping myself motivated and getting myself to write. Does anyone have any ideas for me, or any help?