My No. 1 trick for writer's block is to open up my email about why I'm having trouble writing. I leave the recipient blank, but usually I have someone in mind, such as my mother, a friend, etc. I find that spending three or four minutes whining about why I can't write actually serves as a warm-up and it usually breaks the ice. I once wrote an entire chapter in email -- and then sent it to myself.
The other thing that I do is to shift what I'm working on. Since I'm a food writer, if I'm stuck on something in the narrative of a book, then I go work on a recipe, either editing it, reviewing comments from my recipe testers, that sort of thing.
What I find doesn't work is mindless online admin. I can get very caught up in returning emails, following up on event details, that kind of stuff. So I try to avoid it.