Getting Back to Writing - Write ANYTHING
New notebooks beg to be written in. Listen hard. You'll hear their call. "Write in me. I am receptive to all your words. All of them."
If you haven't written in a while and you're not quite ready to commit to the next big WiP, my best advice is to write anything you damn well please. A random scene, a "missing moment" from an old story you love, crossover conversations between your characters from different projects, flash fiction, short fiction, fanfiction, a blog post... Anything that involves creative thought onto a page.
It doesn't have to be good. It doesn't have to be a part of a bigger thing. It just has to be words. You can always hold onto it and expand on it later, especially if the idea pokes and prods you when you least expect it.
I have a lot of notebooks with snippets of stories in them. I think of them every now and then. Maybe someday I'll go back and dedicate real time to them, but I don't have to. The simple act of writing those snippets helped me find my way back to a big project after a long break. And I also have my "Things I'd Like To Write" notebook. Oh, and my Character Bank!