I've replaced a lot of my normal web surfing time with putting in some bluetooth headphones and listening to audiobooks. Much more fulfilling than spending hours on the internet where I can't even remember what I did that whole time, and you're freed up to do other things like work out, prep food, clean the kitchen, etc.

Not sure if it has improved my concentration, but it has improved all sorts of aspects of my life in surprising ways. Like I'm now the type of person who doesn't mind hand-washing all the dishes where, in my 20s, I'd let them pile up in the sink—I just do it while listening to a book.