If I were to give a single piece of advice for easier journaling it would be this: make it handy.
By “handy” I mean “convenient and unceremonious.” It’s best when it doesn’t take more than a few seconds to bring it up and start writing. And, the straighter the line the better: I mean if I have to navigate through a complex UI, with a lot of icons, menus, and text, it may very well happen that I just forget the dear idea that I wanted to write!
I use the built-in iOS Notes app. I can conveniently put a “New note” button on the Control Center which means that anytime I want to jot down something, it only takes one swipe from the button and one tap, and I have a new note ready to type. On my laptop, and, on any computer really, there is an infinite number of possibilities.
The most important thing is to quickly write down the core of the thought: enough words, letters, or symbols to be able to remember what I meant later when I review the notes during the day and flesh them out.
Then, when I review them at the end of the day, I process each of them: move it to the appropriate place in my system, delete it, plan a writing session to expand on it, or something else.