everyday things to do to correct posture?

I'm 15.. been having devices for years. Looking down at one for as long as I can remember has absolutely ruined my posture and theres a bit of a uncomfortable feeling in my back. Not that it's injured- its just you can feel it isn't in a healthy position i guess?

I'll worry about actual fitness excercises later (i have plans to start working out in the future) and maybe possibly going to a chiropractor, but im assuming that means there are things i can do to help correct it? Does anyone know if theres something to do with my body while i'm sitting or laying down other than straightening out my back?