I am working on a graphic novel and I can tell you that the best thing for you to do is to make sure that you have blood pumping through your body so take exercise breaks one of the things that Dan Brown did was he hung upside down from the bars and pull ups I mean you can exercise do yoga take some breaks.

Also when you are writing a book or even in my case making a graphic novel always always always have a skeleton for it because that always makes it easier and you won't get as stuck.

Have someone proofread it like maybe somebody on here or one of your friends.

Anyway that's my two cents I'm really excited to work on my book too, good luck to you!