When I leanedlearned Spanish, I found the best way to improve my vocabulary was reading books. Try to not to look up every word you don't know, but rather pencilwrite it down and keep on reading, trying to get the gist of the words from the context.
Only after having finished a number of pages, look up the unknown words and write them down with their translation. Start with books where you already know the story and that are of interest to you, just try to make sure you still have joy in reading - don't loose the plot while looking up words, keep on reading. Everything that is sort of entertaining will make you learn at least twice as fast than some boring language learner's book or other specific literature.