That is so exciting- congrats to you on your big project, Heather! 
I know there are several creativity and motivation spells around here, but the ones I’m thinking of are geared toward restarting after someone has hit a creative block or needs some more inspiration. I’ll drop some links just in case- they can always be adapted to your needs!
Crea-tarot-ivity: A Motivational Card Spell
Motivation and Creativity, Come My Way Spell
Jan and Amethyst have already given some excellent advice- the only other thing I can think of to add in is to consider the space you are writing in! I’ve found that going to a working cafe, co-working space, library, or study center (anywhere where other people are also writing) helps to tap into the “hive mind”. When others around you are being productive, it really helps you increase your productivity too! 
Oh! And another psychology-based note on space- they say to sit in a big, open room or outside when you want to think of big, overarching ideas (like main plot points) but to sit in a smaller space with a low ceiling when you want to hone in on the finer details 
Good luck and happy writing, Heather! 
