My next aim for studying English

My stay here in the U.S. is going to be 3 months. I can feel my English conversation skills both speaking and listening have considerably improved. To improve my English, I’ve been spending my time to listen and speak English sentences in CDs. As a next step, I am thinking to focus on studying vocabulary which includes words and idioms.
I consider better vocabulary also improves the conversation skill. So I am using textbooks for that when I have time. To remember English words and idioms which I don't know, translation from them to Japanese, my mother language would be the best way. On the other hand, remembering them only in English, looking up those meanings only in English dictionaries, would also be one of the methods. In this case also, thinking of corresponding Japanese meanings would help understanding.

I’d be glad if anyone corrects my sentences.
Thank you.