Journaling gets abandoned within a week when it is treated as writing, something to be good at. It works better as a way to empty your head for a few minutes, with no reader.
Your first day
Grab any pen and paper, or a notes app, and set your phone's timer for five minutes. Write about today, starting with whatever's first in your mind, even if that's just "I don't know what to write." Keep the pen moving the entire time. Don't go back and read any of it until the timer ends.
Most people stop mid-entry to cross out or fix a sentence that came out wrong. Don't. That single habit is what turns journaling into an assignment instead of a release.
The thing most people miss
It's natural to assume a journal should produce something worth rereading. But the entries that help are usually the messy, unedited ones, because editing is what turns the exercise into a task.
Stop trying to write well during these minutes, and stop treating grammar and legibility as things that matter here, and the notebook stops being one more thing to get right.
A misconception worth correcting
A journal entry doesn't need to be legible to someone else, or even to you a year from now, to have done its job. Fixing a sentence mid-entry doesn't make the entry better, it just interrupts the one thing the five minutes was actually for.
A single question written at the top of the page, such as what is on my mind, is worth trying once a blank page stops being enough on its own.