I'd second the recommendation for Farber's book. It doesn't try to hide that you will need to work, but the work can be enjoyable and productive - that's the se

I'd second the recommendation for Farber's book. It doesn't try to hide that you will need to work, but the work can be enjoyable and productive - that's the sense of the word "easy" in this context, rather than "work-free". It also recommends some techniques for memorisation and has some great anecdotes from Farber's own language-learning experiences.