The Art & Science of Journal Writing

The concept of keeping a journal is relatively simple.  You just write. Right?
But what makes your journal ever so more meaningful and important to you is that you:
Write often.
In your own voice.
Peeking below the surface.
About important stuff.
How do you do that? 
Consistently. 
Playfully?
Seriously!
Passionately…
With [...]