In my personal experience, keeping a journal of your mediations can be very important, just like with any other magickal workings.
Some people keep a journal or diary. Others don't. But when it comes to any kind of spell casting, rituals, meditations or even astral travel, i have found them to be very helpful. I know for a fact, that any attempt at meditation or astral travel (for me) under a full moon will not work. I simply can not gain the level of concentration required.
This will be part of your personal journey, because there is no "right" way to do it. You may choose to keep a journal or diary of your personal expereinces with meditation, very detailed and story-like. Or you may choose a "just the facts" approach recording the day, time, and goal of your mediation. Many followers of the goddess will incorporate the meditation entries into their Grimore (Book of Shadows) and be very detailed.
My method:
In my case, i have keep a Grimore. A Grimore is a personal book of shadows that contains my deepest thoughts as well as an accounting of my magickal workings. Each day, for each task performed, i will record the date, the time, phase of the moon, temperature and weather. This helps me to see where i succeed and where i fail with certain types of ritual or study. In my case, it is kept in journal format.
I have two journals. One is computerized that is my thoughts, hopes, dreams, ideas and other things about my day to day life.
For my magickal work, rituals, spells, dreamworking and meditation, i keep a hand written accounting. There is power in words and more power when those words are written by hand. Upon my passing, these tomes will be passed to my children and loved ones so that they can see in my own hand, the type of person that i was, i am and that in the end, I became.