An often overlooked strategy for helping students improve their pronounciation is working with the International Phonetic Alphabet. Phonetics is a website created by the University of Iowa that has been around for many years and that explains what the sounds of American English are and how they are produced. For every phoneme there is you get an interactive diagram of how that sound is articulated, audios with the sound itself, and sample words where the sound occurs.
The only requirement for you to make the most of this great tool is to keep your Flash complement updated. There is also an app available for smartphones. Learn a little bit more about Phonetics in this video.