Your question reminded me of this blog post, The Korean's English Acquisition
, by a guy who moved to the U.S. when he was 16 and didn't know any English. He made flashcards for every word he came across that he didn't know and studied a group of 50 until he memorized them all. Then after memorizing five groups of 50, he practiced all
of them (i.e. 250 words) again. He says that by the time he graduated high school he had memorized over 30,000 words.
It's not the most inventive or fun way to memorize, but what you can take away from this is that it takes time. Try not to be discouraged; memorization is just something you have to do