Neck or back pain
Most people have their font set smaller then it should be. Just because you can see it doesn’t mean you can’t set it at a larger font to see it with less strain. The more magnified the font the less you strain your eyes to see it.
Set The Light Right
Eye strain is often because of the lighting on your device. Make sure the light on the screen of your mobile device is light enough for you to see without squinting, but not to bright.
Take a Break
Look away from the device. I was told that every 20 minutes I should look away from the screen to a distant of 20 feet for at least 20 seconds. The 20/20/20 rule gives your eyes a chance to refocus.
At a Distance
Hold your device at a distance. This also helps improve the way your eyes focus on the device. The closer the device the harder your time your eyes have to focus on what your reading.
When we are focusing on the screen we blink 2 to 3 times less then we normally do. Because of this our eyes can become dry. Make yourself blink.