you better not be a teacher. 'cause your students are not a good hand

I think your question is "what's the most effective way to improve students's English in a month?". People could write a doctoral dissertation for that. Anyway, I think the most important thing to learn a foreign language is to listen as much as possible (with different accents) and to imitate just one of them. As for vocabulary and grammatic things as MiXu mentioned, it's just a matter of time and persistence.

I am sure people will have different ways of learning that fit their preferred learning style. I always try to build my vocabulary and learn sentence structure first when leaning a new language.