Wow! Four hundred pages? I wish you the best of luck.
Somewhere along that story, you will witness intense writer's block because it is very hard to keep at writing without getting bored of it or stuck. To overcome this problem, schedule a certain time to write on a regular basis. That way, your mind will be set in the mood to write, so it's harder to get writer's block. Even if you don't write at that scheduled time, make sure you're doing *something* like reading or outlining or drawing your characters.... Something productive that's part of your story.
Carry around a notebook, and eavesdrop on conversations. Hear how other people speak, so that dialog and character behaviors may become natural for you to write. Even if your character's are animals, they will still have human traits. Otherwise, the story will be boring. Make sure you jot down your dreams right when you wake up before you forget them! Dreams are a great way to keep yourself motivated or inspired while you're writing your story.
Write about things important to you. Don't write about what your family's interested in. Write what YOU'RE interested in. You know what you like, not what your family's likes.
Most importantly, do not give up. Keep writing, and put your whole effort into it! Good luck! =D
