How does it help you go lucid? Well while you journal you have dreaming on your mind. It is like a form of MILD, because it's the sort of thing, that suggestion that carries over into your sleep. Incedentally, as you read about lucid dreaming right now, you are actually improving your own chances of having a lucid dream. And the people who journal also seem to be the ones who "Go lucid for no reason" most. This is closely related to MILD. Though I've never approached MILDing with much dedication, it is along the same lines as it as far as I can see.

But really the explanation almost goes off on a tangent. I'm pretty sure it's accepted that dream journalling will aid you in your ability to go lucid.

It improves your recall yes, but somehow, and I don't know how exactly, it makes you a better dreamer while inside of the dream as well.