Plan out everything you wanna write such as a topic. I always set up a topic that I wanted to talk about every day and add more addition note about unexpected things if I want to.
I just have different styles of journals from reck the journal, to an composition notebook which I keep next to my bed. One in the car and a small one in my diaper bag.
Unfortunately, I have had great trouble writing in my journal systematically. But I now use an app… Mood notes… That reminds me daily and I've timed the reminders for my daily commute to and from work. I find my trainride perfect for reflecting on my night (I'm having trouble sleeping and am trying to figure out why) and on the day ahead of me. It helps me at the right mood and mindset and to remind me of my daily habit goals.