It's easy to plow through the days, never looking back. This seems like good thing as we think of progress as forward-moving. Taking a moment to reflect on where you've been can be helpful, and I was reminded of this as I read this post by Claire Blackshaw.
Some studies show that you can learn and remember more by spaced repetition. Applying that to your life by occasionally revisiting the things you did, dreamed of doing, accomplished, and worried about seems interesting.
Learning to recognize patterns in the kinds of things that bother you but ultimately aren't worth worrying about.
Reminding yourself of the things you want to do while you have time. It's sobering to realize you've been wanting to travel, start a company, spend more time with family, or write a book for years.
Realizing how much you've accomplished. It's easy to feel like you're falling behind. I don't spend time thinking of the apps I've built from scratch or the people that have sent me kind words; the list of things to do spins about my head like a child's mobile, occluding the horizon.
Maybe there are more. I'm going to try to do more lightweight reflection and see what happens.