You wrote down 50 words from a dictonary or from a book, wrote down their translations on another piece of paper or another side of the card. Then you embarked on the course towards the noble goal of memorizing them. Unfortunately, you probably have dropped the whole idea rather fast. You may have lasted for some time if you are obstinate enough. A comment by Alexander Z .
Cards are very good for studying grammar.
For English I have about 400 cards. Then I put the cards in random order and, taking one, try to recognize an English construct. Since the phrases do not have a fixed order, I cannot just memorize the answers by rote. You might have tried some tricks. Revising the whole set of words periodically.