There are no rules, really; make to-do lists, write reflections, do free-writing, doodle–whatever works for you.
The best thing about keeping a writing journal is that you can customize it according to your needs and schedule. There are no rules, really; make to-do lists, write reflections, do free-writing, doodle–whatever works for you. You could keep your log on a notebook, planner, notepad on your phone, sticky notes, and so forth.