It's funny... The more I journal, I find the less I know about journaling.
How's that for irony?
I'm not kidding.
I find that what works for me in this moment with journaling may or may not work for me in the next moment. What has worked for me earlier, might not work in this moment.
There is one hard and fast rule that never fails: Just journal.
Also, this form of journaling is always best and never goes out of style: The SOC form of journaling. It's the Stream of Consciousness Journaling, capturing it all on the page, throwing up on paper, just journaling, writing practice (see Natalie Goldberg), and is what some call morning pages (see Julia Cameron).
The SOC Journaling is hands-down the one I recommend most. In fact, I recommend doing this at least once per day, but multiple times is far better.
Do you want to know how to journal? Always return there to the SOC. You will never go wrong if you do.