In my case?
Take occasional mental breaks!
Working yourself to exhaustion is bad for your health and your creativity.
Just by takinga few minutes every hour or so to relax, listen to music or read an article help boost your creativity. It could be exactly what you need to get over that last mental hurdle. Also, knowing when to keep working and when to take an extra five minutes to get up and stretch or just move around is is really good for you.