Suggestion: Helpful Hints
Below the lesson boxes some subjects have helpful hints but most do not. I really appreciate these hints and wish that they would be included in more lessons. Where they are missing, and where I most need them, is in the subjunctive cases. I just started the "Past Imperfect" lesson but I have no idea what Past Imperfect is! A little description to go along with a few more of these lessons would be a big help. Okay, I looked up Past Imperfect and now I'm ready to go back to work.
The internet really is awash in resources (good and bad) and the forums tend to be a good place to find suggestions. The Duolingo wiki Spanish page has a long list of resources that others have found useful, and it deserves to be shared more! I highly recommend StudySpanish.com, SpanishNewYork.com, and DrLemon.com for starters.