The whole site has well-stated ideas, but I think the finite principle
is my favorite one.
I'm gradually breaking the habit of constantly checking things. I'm at the point at which I do not look at my phone in my bed when I'm going to sleep. I'm also coincidentally able to sleep better more coincidentally.
A big help is that when I do check my phone, there's not that much there. If it's one of those days when I'm checking each hour, there's like one email and five RSS posts for each check. I read those, then I can stop.
Twitter, et al, basically make sure that you never stop, that there is always more shit for the lizard brain part of your brain to seek.