One of the best and most practical breaks is walking. For cerebral work, just a 5–15-minute walk has been shown to increase creativity. For physical work, a brief walk encourages one’s heart-rate to come down while keeping blood flowing and the body limber.
The main takeaways: 1) Don’t multi-task — even if it feels productive, it’s destructive. 2) Remove distractions. If you’re unaccustomed to working in this manner, start with small chunks, even as little as 10 minutes, and gradually increase duration.