Unfortunately there is no magic trick to keeping a dream journal... you just have to force yourself to do it.

I know it's tempting to just tell yourself that you'll remember it all in the morning and that you'll write it down later... but the truth is you won't remember it all. I fight most mornings to make myself write down my dreams and when I lose that fight, I inevitably lose most of the details of my dream as well.

So keep a pad & pen or a tape recorder by your bed and take those few minutes to capture your dreams the second you wake up.. even if it's just a few key words.. you'll be glad you did.