You really should keep a journal, according to everybody everywhere. I agree; my journal comes with me everywhere I go, and I know it's helped me in all kinds of ways. It's hard to know where to start, how to keep up with it, or even what the point is, though. The simple act of writing is a little anachronistic in an age where, instead of sharing our thoughts or feelings we can repost somebody else's words superimposed over a picture of somebody else's cat. It matters, though. Trust me on this. Having trouble getting in touch with your feelings? Keep a journal. Want to get better at expressing yourself? Keep a journal. Interested in getting out of have-to and into want-to? Keep a journal.
There's more to be said, of course, but five minutes googling for "benefits of journaling" can get you further than I can here. Besides, you already know all of that. The question tends not to be why one ought to keep a journal, but rather how to get started. I struggled with that for a while, too, but then I found out about Microjournaling. Please give it try for a few days; you'll love it. I found that it helped me get to a "hmmm" state of reflection every day, and, as a result, I was better able to move forward with the things I wanted to do.
The tools of the trade don't matter much; please find what works for you. Some people use their phones or computers, but I'm an analog guy in this respect. I use a silly, leaky fountain pen. I carry a Traveler's Notebook with me with two inserts. The first insert is graph ruled for the mind maps I use to prepare Sunday lessons, classes, and presentations. The second insert is blank, and is devoted exclusively to my microjournal. I've been doing it for a while now, and I'm a fan.
What works for you?