1. Research shows that the vast majority of words are learned from context. To improve your context skills pay close attention to how words are used.
2. 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.
3. Say the word aloud to activate your auditory memory. Relate the word to words you already know. For example, the word GARGANTUAN (very large) has a similar meaning to the words gigantic, huge, large, etc. You could make a sequence: small, medium, large, very large, GARGANTUAN. List as many things as you can that could be considered GARGANTUAN: Godzilla, the circus fat lady, the zit on your nose, etc. Create pictures of the word's meaning that involve strong emotions. Think "the GARGANTUAN creature was going to rip me apart and then eat me!"