Keeping a meditation journal gives you a history of your practice to reflect upon. It enables you to identify trends or patterns that might otherwise go unnoticed in your day-to-day routine. In short, it helps you learn more about yourself and your relationship to your practice. Try keeping your own meditation journal but don't meditate just to write it down. Use the journal to record challenges and also successes. See what works and build on that. Watch how your struggles diminish over time and also how your mind gradually changes.