What I do for myself, I try to pick up three or four words every day and first of all, I look up the definition, then I make my own definition to the word (very often an image) and then make sentences with the new words. Say my yesterday word was of Latin origin "vade mecum" means a small book reference book which you keep in your pocket. My definition was a small worn-out book, which an architect kept in his pocket and kept referring to. Sentence: "His vade mecum was his Bible, he could not concentrate on his architectural works if the book was not with him!" Hope it helps ;)

Try forming senteces where you use those words. Full sentences are much easier to remember.

Don't just memorize but try to use/apply the word regularly. :)

How to learn more difficult vocabulary? You need a good teacher to judge which level of English your vocabulary is and then to guide you. There are different levels and you should pick the next level and concentrate on it with emphasis on which category of that level is suitable/useful for you. Then you need special techniques that help you to make that higher level of vocabulary a permanent part of your active vocabulary. You do not need to buy books. I can help you. John

Try this www.memrise.com. It'll blow your mind.