I think the reason why people are unable to keep a diary is because of the feeling of obligation. Eventually, it becomes a chore and the whole process feels kind of awkward, like you’re expected to pour your heart out into your notebook. The typical image is one of a person lying in bed at the end of the day and recollecting all the day’s events. On the other hand, when it comes to a journal, it’s basically just a record of your experiences, thoughts and maybe feelings, as and when they come to you. And that’s exactly the approach you should take to journaling.
Don’t try to organise your journal. Don’t try to make it look a certain way. Take down notes in point form, write in long prose, draw diagrams, doodle (doodling actually helps reflect your inner thoughts quite well!) – whatever comes to mind. Just ensure that things are put down onto paper. And remember to date all your entries!
If really nothing happened that day, that’s when you can do the whole lie-down-on-your-bed-and-reminisce routine. That is, if you’re determined to have a journal entry each day.
At the end of it, your journal will be an eclectic mix of different writing styles, maybe even handwritings, and different presentation methods. But it will serve as the most accurate record of your thoughts and experiences. Don’t overthink!