These are surely some useful tips, but I always tell my nephew and niece to avoid phone usage as much as they can. Having a bigger screen like desktop, laptop or even tabs, is far better than doing everything on a phone. I will be 30 in a few days, so yes I was part of an era when paper and books were preferred over electronic media as far as reading/writing was concerned. Yes, technology wasn't that great during those times, but still we did have options. I am at work as we speak and I still have my pen and paper with me all the times to take down notes if an unscheduled meeting comes up or something. I do see people and specially kids, trying to manage their whole lives using a phone, and I really don't prefer that for myself.

However, I do understand all of us might not have the liberty to move away from phone even if we want to, due to time or portability constraints in general. So if you really don't have another option but to carry out most of your tasks over a phone or a tablet, do follow the aforementioned points highlighted by @greenrun

Having said that, I strongly believe we can cut down our entertainment-related tasks over a small screen! Games, YouTube, Movies, etc... I mean why guys? :/ Isn't it better and more fun to play a soccer game with your old friends than sending them invites over a mobile app? Isn't it better to have a movie night with your family on a weekend than watching it alone in your bed? My point is.. whatever you can avoid over a screen, do that. Don't let controllable and avoidable things be part of your routine usage of these digital gadgets out there... Technology can and will be replaced every year, your health won't.

Just a thought. Cheers! :)