Ask HN: How to develop an ear for grammar as a non-native speaker?

My English skills were quite mediocre few years back. I made lots of mistakes and my punctuation was terrible. I believe I have grown considerably since then. However, I still find myself making grammatical mistakes and forming sentences that sound unnatural. A sentence like "Why Amazon is so great?" doesn't sound wrong to me at all; a native speaker, perhaps, would see the obvious mistake. It often becomes incredibly difficult for me to decide between two choices for a sentence, as both sound correct; yet, I can feel there is something amiss. English Grammar is pretty complicated and it's an impossible task to mentally organise a complex sentence into its constituents (subject, predicate, conjunction, determiner..). Apart from reading, what can I do to develop an ear for Grammar? How can I learn to avoid conspicuous mistakes?