Reading: Books boost your vocabulary whether or not you stop every 10 seconds to look up a word. So instead of torturously plodding through some famous piece of literature with a dictionary, do this: Find a book in a genre that you actually like (The Harry Potter translations are reliably great!) Find and read a chapter-by-chapter summary of it in your target language (you’ll often find them on Wikipedia). This is where you can look up and make flashcards for some key words, if you’d like. Find an audiobook for your book. Listen to that audiobook while reading along, and don’t stop, even when you don’t understand everything. The audiobook will help push you through, you’ll have read an entire book, and you’ll find that it was downright pleasurable by the end.
Reading to deepen understanding suggests any book and go through, find online chapter summaries in target langauge, listen to audiobook while reading it, as it forces you along.