Howard Abrams has an excellent post on journaling with Emacs and Org Mode. The post documents how his use of Org Mode evolved over time so you can see what (at least for him) worked and didn't work. That's very useful for figuring out your own strategy even if you settle on something different from what he did.
One of the things I like about his approach is that he uses
org-capture to make his entries. That's nice because no matter what you're doing you can pop up a capture buffer, make a quick entry, and go back to what you were doing with very little effort. That makes it easier to maintain the journal because it's almost frictionless.
Another nice thing I learned from his post is autoinsert. It allows you to automatically insert text to the start of a file when you first create it. It's another in the long list of ways that Emacs can make your workflow more frictionless.
Even if you're not interested in maintaining a journal, you should give this post a read. You may learn a useful technique or two.