I've found two things helpful over the years. 1) Read books. When I'm staring at the monitor for hours my eyes don't move around as much and my eye muscles can

I've found two things helpful over the years. 1) Read books. When I'm staring at the monitor for hours my eyes don't move around as much and my eye muscles can get weak which leads to headaches. I've found that simply reading books forces me to move my eyes around enough to correct this. 2) Go for walks outside. When you're walking around outside you'll need to refocus your vision on things at all different distances. This has helped me a lot.