Whenever I'm not at my computer, I think, "I really want to write". Then I get to my computer and get paralyzed with anxiety, then get distracted by something else.
There are a couple mantras from Anne Lamott's book on writing, Bird by Bird, that I repeat to myself when feeling anxious or stuck or easily distracted. One is, short assignments. The other is, shitty first drafts. For me, they help remind me to just write something. Don't worry about finishing the book, the chapter, even a page. Write a sentence. And don't worry about whether it's any good.