Make the entry small enough to finish
A date, a route, a duration and a few words about the outing are a useful start. Add distance if it matters to you. A short note written regularly is more informative than an elaborate page you only complete on exceptional days.
Separate the plan from the record
Keep what you intended to do beside what actually happened. A changed plan is information, not a blank space to hide. Work, travel, weather and rest all belong in the context around your running.
Review with a question in mind
Look back for practical patterns: which meeting time was easiest, which route felt most welcoming, or what helped you get organized. A journal can inform a conversation with a coach; it does not diagnose pain or prescribe a training load.