Nearly every abandoned journal was abandoned for the same reason. The entry was too big. Not too hard to write, too big to start.
Make the entry smaller than your resistance
A page is a project. A line is not. If the smallest allowed entry is one sentence, then a bad day still gets logged, and a bad day logged is worth more than a good day written beautifully, because the point is the run of them.
Log first, write second
Put down how the day went before deciding whether you have anything to say about it. Most days you will not, and that is fine, the record still stands. Some days the writing arrives on its own once the tap is done.
Attach it to something you already do
Not a time of day, a moment you cannot miss: the walk to the station, the kettle, putting the phone on charge. The habit needs a hook that already exists.
Do not backfill
A gap of four days is not a debt. Reconstructing it produces a tidy record of days you cannot actually remember, which is worse than the gap. Log today and carry on.
Read it back, or have something read it for you
A journal you never reread is a pile. Reading back is also the least likely thing to happen voluntarily, which is why it is worth having something that does it on a schedule.
What this looks like in Dayglean
An entry is a tap on one of five moods. Writing is optional. From the home screen widget or an Apple Watch the tap takes about a second, without opening the app, which is the version that survives a busy week. Once a week the app reads the entries back and gives you one thing it noticed.
Dayglean
A private journal for iPhone, iPad and Apple Watch. Tap a mood, write a line if you feel like it, and once a week it hands back one specific thing it noticed in your own entries.