I have several Moleskine cahiers on my desk, the first dozen or so pages of each filled with text. Though the pages are blank beyond that point, I prize them. We've taken these on some important trips in our lives (a summer in France and a week in Peru) and those pages have details - mundane - that I would have forgotten otherwise.
For example, upon arriving we hopped in an old Volvo for our ride to the hotel, our driver pointing to some things on Avenida del Sol. That night we heard a song by Julieta Venegas in the hotel.
These details aren't necesarily crucial; I remember the trip fondly without them. But reading them again is valuable; in some cases it's like a light shining into a dark corner, calling to mind things just out of reach. Other times my own words seem completely foreign - they're the only proof some of these incidental things happened.
I make journaling apps but haven't kept my own journal very well - it's a spotty endeavor, marked by fits and starts, periods of daily entries followed by silence.
I recently decided to try again. I now write daily, starting in the morning and continuing, perhaps, later in the day. I'm still figuring out what I want to write about, but to get in the habit I simply allow myself to write anything, even just a few sentences about the morning. I figured if John Adams could get away with a few one-word entries about the weather in his own journal I could too.
I written every day for over a month.