Via ZenHabits:

Have a disconnect time each day. It’s like setting office hours if you’re a professor — you set the times that work best for you, and you can even let people know about these times. Let’s say you are disconnected from 8-10 a.m. each day, or 4-5 p.m., or even anytime after 2 p.m. Tell people your policy, so they know you won’t be available for email or IM. And use this time to create.