If you can read English, but can’t understand Americans when they speak, a series of apps called “Learn English by Radio” is really helpful. The audio can be played at either original speed or a slower speed. The slower speed really helps you develop an ear for English. Also, there are lots of links to idiom, vocab, grammar, and pronunciation clarifications. The apps are based on American radio shows like Dragnet and Gunsmoke, so are fun to listen to. You can find them on the iTunes store- they are by a company called MapMuse.