I started journaling after reading
The Artist's Way by Julia Cameron. She advocates a technique called "Morning Pages" and just writes 3 pages every morning about whatever comes into her head, kind of like free association when in therapy. But getting in the habit of just writing gets that out of the way so you begin to notice things and enjoy the writing experience and then you can start paying more attention to what you're writing than when you just begin.
http://paperartstudio.tripod.com/artistsway/id3.html