I'd suggest you find 3 or 4 journals you really enjoy and pay attention to what makes them so interesting. You'll be ready to record the sorts of details you'll need for a high quality journal entry at the end of your day on the bike as well as what sorts of pictures to take.
+1. Impressions of ppl you ride with and meet along the way. Accounts of how you interact with your riding partners and strangers. Characterizations. Quotes of interesting conversations you have. Personal angst, trials and tribulations. The highs and lows of the ride.