Flashcards are good. They're even more effective when supplemented by the following exercises, which my foreign language teachers always required of me and which I now always require of my test-prep students:
For each new vocabulary word and idiom:
- Write a series of sentences that use the word/idiom in its various contexts (e.g., I prefer NOVELs to non-fiction; and mixing chocolate and peanut butter was a NOVEL idea.)
- Use those words in conversation that week