There are many things you can do. But here are two I tend to do.
1. have a second story in the side lines and write a bit for that 'til the other story comes back to you. It's fun but can be frustrating when you have two stories going you have to get done. What happens when you get stuck on both of them?
2. you can read and review, nothing beats getting stuck into another writer's work, and I find writing a good/great review can be hard but it can unlock that part of you as a writer that has gotten stuck.
So this week when I got stuck I picked up the ARC Milly asked me to read for a review and I jumped right in. Not my normal sort of read but I gave it a go and loved it. Now I am ready to jump back into my writer's seat and get back to where I was with Portal. I know there is nothing up on the site yet of Portal but I hope around Xmas I will get the first chapter up for everyone to read. But I do have little bits up on the Facebook page so feel free to take a look. (links up top!)
Lots of love, your writing friend,