Here are a few things I have learned about keeping a journal:
1. Do write the date, time, place at the top of every entry.
If you want to get really creative write the moon phase and temperature too.2. Write everyday.
3. Don't be afraid of your feelings, until you put them down you never know what you really think.
4. Review every few months.
If you carry your journal with you, then that five minutes of down time can be used to write, even if it's good or bad times, you can make a note of it. Keep writing until you feel grounded in your life, comfortable, confident, and happy.
After years of keeping journals and reviewing the progress you have made you can feel pretty good about your efforts, and remember where you were and what you were doing. Maybe they won't make a movie about you, that's not the point; keeping a journal is good for your mind. Keeps you on your toes and thinking, growing, learning. Try to write something different everyday without repeating yourself. Watch your creativity grow.
here is a link that is more in-depth than I am covering here with some good ideas.