I didn't have the book that came with my deck, so I feel your pain with trying to remember them... so this is what I did instead.
With every card, I wrote down what it meant to "me" - not what the book said! This gave me not only a personal connection to the cards, but also allowed me to memorize them a lot easier. When I got a solid grasp on what they meant to me, then I went back and learned the core meanings at my own pace and added to what I already knew. Turns out, I was really not far off most of the time.
It helps if the deck of cards you have are illustrated too, then you can go with your intuition.