Lucid dreaming is when your aware your sleeping and your dreaming and taking control of your dreams. Yes keeping a Dream Journal is very helpful. When you go to bed right before you fall asleep tell yourself that you will realize it when your dreaming. Once you do this for the first time you should wake up right away. When you do wake up immediately grab you journal and write down what your dream was about.
What Sue suggested is very helpful. I would also recommend meditating on what you wish to accomplish through lucid dreaming. This should be done immediately prior to laying down. I find it helps me to focus better when I do lucid dream. Best wishes