Keep a small notebook with you at all times to write down any ideas or observations you think are worth remembering.
Transfer the notes as soon as you can to a permanent notebook. Organize this notebook into sections. This could be by date or topic, such as poetry, song lyrics, reactions to something in the news, or significant family events. Items could even include headlines or articles from newspapers or magazines. Use a glue stick to attach such items to the book pages.
Write down the date of each item entered in the book. Even if you are not keeping it in chronological form, the date could have some meaning when you go back to study the entries.