Write about three things, and three things only:
- What you did
- Who you did it with
- Little observations along the way
These are the three most cherished memories in petrified form. Write more than this and you may burn out, miss more days or take to brooding.
A blog is different. A journal or diary is highly personal and will be of great interest to a few people. A blog is fairly impersonal and will be of moderate interest to a broad audience.
Inspiration: http://artofmanliness.com/2009/06/07/30-days-to-a-better-man-day-8-start-a-journal/