I recently learned that iPhones show a breakdown of how much time you've spent on each app in the past seven days.
The first time I stumbled across this, my numbers were...not good. (14 hours on Twitter! I don't even LIKE Twitter, and I definitely didn't think of myself as a power user!!!) Now my friend Brett and I have a standing Wednesday night appointment to screenshot and share our numbers from the previous seven days with each other. It's been interesting (if slightly embarrassing) to track, and it's a great reality check if you're feeling too busy to do things like reading or writing or getting enough sleep. (To see yours, go to Settings > Battery. Give it a second, and a "Battery Usage" widget will load at the bottom of the screen. Toggle to "Last 7 days" and tap the clock.)
A couple weeks after checking out my numbers regularly, I started using the Forest app, which lets you set an amount of time to not be on your phone, during which you start "growing" a tree. If you check your phone before the timer is up, the tree dies. It's really helpful for those times when you want to focus but keep picking your phone up out of habit. Definitely recommend.
(P.S. I am now down to less than three hours a week on Twitter!)