Oh my goodness, making flashcards. Pick a couple words every day and then be sure to use them throughout your practices.

Reading newspaper articles, short stories and later novels will help you expand your vocabulary. If you write down the sentences containing the new words or if you make sentences with the new words, you can learn to use them without having to memorize them.

Reading widely helped me when I was learning English. I read the newspaper, novels and short stories. Perhas if you are not a fan of reading, you could try watching films or listening to the radio and every time you write down whatever you did not understand and look it up. Start keeping a notebook with sample sentences for your new vocab. I usually combined as many of my new words in one sentence instead of forming one sentence for each new word, that would take too long. Using words in a context that you can easily understand makes it easer to remember them. This is just from my experience.

The best way to build a good vocabulary, regardless of whether or not you are learning a new language or mastering your own, is to keep practicing the four core language skills. You have two different types of vocabulary: Passive recognition(reading and listening) and Active utilization(writing and speaking). Practicing just the passive skills will make you a better reader and listener, but you will still struggle with the active skills. This is what I do for new vocabulary: 1) Identify new word that I do not recognize and look it up in a dictionary 2) Find other examples of the word 3) Write the word down in a book and start trying to implement it into my Writing and Speech. It will take time and effort to build up a sizable vocabulary, but keep trying little by little and you will have a collection of words with which you have a strong understanding of :) Also remember this: Memorization without utilization is not lasting. In order to harvest a crop, you need to not only plant the seed, but also till and water the soil. Hope this helps :)