Why keep a work journal?
Throughout history, intelligent people have kept records. Scientists keep a log of their experiments: what they tried, what they expected, what happened, and what went wrong. Pilots and ship captains keep a log to record their course and provide a record of their activities in case something should horribly awry. Authors often keep a journal of experiences which they might draw on in their writing. Philosophers, social critics, and other thinkers may keep a journal to draft ideas, and record what is on their minds.
Why should you be any different? Work like a scientist (or, if you prefer, a starship captain). Write things down. It helps you think, it records your course of action, and having those thoughts and actions written down may be useful if a course correction is needed down the line.
Beyond being a record of activities and intentions, a journal is is also a powerful tool for providing focus. It provides you a safe space to type things out while you start to gather your thoughts about them. Doing so encourages planning, strategizing, and forward thinking. Writing short, simple journal entries each day helps me keep my eyes on the big picture things, and encourages me to add perspective to my activities and to-dos that a task list never could.
What is a work journal?
A work journal is a private, informal way to structure your thoughts and plan for the day, week, or month ahead. I have kept them, on and off, for years. I have used various apps and services to keep work journals, but I have settled on plain text files these days for their simplicity, portability, and the variety of text editors I can use to work with them.
A work journal, for me, is just a plaintext note I create at the beginning of each day. I name them all the same way: "Journal yyyy-mm-dd.md" (where yyyy-mm-dd is the date, of course). (If you don't want to bother creating a new file every day, you can just use a single text file for all of your journal entries, and write the date above each entry.)
I then write a quick message to myself about what I have to work on and accomplish for the day. I often list out the projects that I have to work on that day, and the main things I plan to do for each. If those things aren't in my task list yet, I will add them right after I'm done with my journal entry. I also write notes to myself to help get me thinking about meetings I have to plan for and specific problems I need to solve. I often write down my thoughts and opinions about what i am working on as well, so it is not simply another task list. The whole process takes me only two minutes or so each morning, and jumpstarts my workday.
This is all "free writing", which means you just write things down for a couple minutes, stream-of-consciousness style. It doesn't have to be spell-checked or even well-written. You don't have to spend time formatting it. You don't even have to do it every day; if you lapse for a while, just go back to it when the feeling strikes you again. It helps to schedule regular review sessions with yourself, and use those as opportunities to get back to writing entries in your work journal.