Learning a word won't help very much if you promptly forget it. Research shows that it takes from 10 to 20 repetitions to really make a word part of your vocabulary.
It helps to write the word - both the definition and a sentence you make up using the word - perhaps on an index card that can later be reviewed.
As soon as you learn a new word, start using it. Review your index cards periodically to see if you have forgotten any of your new words.