I really like the use of tools that make focus the default, low-motivation option. If you're not on a Mac, Firefox has LeechBlock[1] and Chrome has StayFocusd[2]. Also, if you're on HN, there are built-in settings under your username you can use to limit how long you can access the site for every few hours.
Ironically, that's why I'm on HN now. I know I only have 15 minutes and then I won't get to use it for another few hours. :)