More specialised language trees
One for listening,speaking and translating
I wish some of the lessons reorganized the question types so that it would be a bit easier to learn (which goes along with the more specialized language trees).
There's one question type where you have to choose the vocabulary word from three pictures. I wish that type of question came first for the new vocabulary I'd learn because then I wouldn't have to worry about forming sentences, or sometimes getting those random phrases that don't translate word-for-word. The next easiest question type (for me, personally) is writing the article (and determining gender) and the vocabulary word with the pictures next to them. After that, maybe I would do a few multiple choice questions with them, and then write the sentence with new vocabulary based on listening, then write the sentence based on the English translation. I think this would allow a more natural progression of learning the basic vocabulary...
Of course, I understand that Duolingo can't possibly fit all that into a 20-question lesson, but I wish I could somehow tailor it that way for myself to use.