Since I am trying to learn German, one of the best techniques that work for me is audio courses. I bought a couple from Audible and they are relatively good.
I mostly use Audible to listen to audiobooks. Amazon has whispersync, which syncs where you stopped on the audio book with what you are reading on your Kindle, given you bought both the audio and text versions of the book.
Amazon also has the same book narrated in English, and German. One idea that comes to mind, what if there is a way to use whispersync between the English and the German version, where I can listen to a book sentence by sentence both in English and German, allowing me to learn the language while enjoying the books I am interested in.
It is a language audio course powered by books.