I suggest just using the dictionary to check the meanings, and picking up idiomatic expressions and vocabulary naturally by reading or listening regularly. I used to look for that kind of ESL material too, until I realized picking up expressions and vocabulary by practicing was much more natural and easy... and it gives the best results.

"Speak English like an American" will teach you how to speak like... an American, ok, but what kind of American? Are you sure it'll be the kind of American that is right for you? If you just practice and pick up the language naturally in contexts you are interested in, your English will improve much more naturally, and it'll be likely to be more idiomatic.
Good luck