How to use electronic devices safely?

I use screens a lot daily and I'm worried it will have permanent eye damage, I don't want to grow up having vision loss or glasses, so how do long is safe to use electronic devices without any effects on the eye in general because I don't want to damage my eyes?

I remember several news stories about eye fatigue.  The reason I remember is the catchy title: "20/20/20"

Every 20 minutes, focus on something at least 20 feet away, for at least 20 seconds.

There are many more tips here:

http://www.allaboutvision.com/cvs/irritated.htm

You should be careful when you use devices because:

1- Technological devices limit the movements of the human body.

2- Obesity!

3- 75% of children between 9 and 10 years are sleep deprived due to the use of devices.

4- Violent content causes aggression for children.