I am trying to learn Spanish and I find that the words that stick are the words that I personally need to use in a conversation. For example, in a conversation with a Spanish teacher we were talking about houses and I wanted to say that we had paid off our mortgage, and didn't know the Spanish word for "mortgage." So after struggling with the words for "pay" and "debt" and "bank," she said (in Spanish) "es una hipoteca." And now I find that it is easy to remember that word.