At a certain point, my mental mode switched. I started to actually enjoy journaling, and look forward to that time each morning. I often find myself journaling 3-4 pages, even having to stop myself "OK, time to actually do some work now."
Like others have said, I stopped journaling about specific events or circumstances, and started exploring my emotions. I got deeply curious about my feelings, and would capture my stream of thoughts. I thought of my "writer" self as the interviewer, and my "emotions" self as the subject. As silly and redundant as it felt initially, I used a "5 whys" approach to explore, writing down the questions and my internal responses.
This verbose written exploration was key for me. It's easy to "short circuit" a thought path and conclude it mentally e.g. "Yesterday, I was angry. Someone did X. I did Y. I guess I probably should have reacted instead with Z. OK next time I'll do Z."
Now I will actually write out the questions and answers as diligently as a court reporter, e.g. "Yesterday, I was angry. Why was I angry? Someone did X. Why did that make you angry? Because it sounds like they think they know more than me about Y. Why does it invoke that emotion if someone thinks they know more than you? Because I don't want others to think I don't know Y. Why don't you want others to think you don't know Y? I guess... I put a lot of my self worth into knowing Y, and I want others to see that..." and suddenly the words become powerful and lead to realizations that dissolve certain "mental loops" that I would get stuck in.