Martyn Jones

The title explains most of this post and is the reason why students who study abroad in a country which uses their target language, will see a great improvement in their ability.  In a country like Japan, where English is almost non-existent outside of the classroom, it is important to expose the students to as much English as possible.

There should rarely be any silences in the classroom.  You can keep repeating target expressions and new words while students are writing, or moving desks etc.

We are lucky with English as a subject because we can use language to describe anything.  This means that we can stick English words all over our school, labelling classrooms, objects, directions, maps etc.  We can fill each step on every flight of stairs with useful vocabulary.  We can create posters about our favourite sports, films, comics etc.  Our students may not try hard to read all/ any of it, but it helps to bring English to life and to get it out of the classroom.

If you often visit a single school, you could even start a weekly English radio show.  This could be as simple as playing English songs, but could also involved recorded interviews with local people who speak good English.
The best educational projects that I have read about all use a holistic approach.  This often involves the local community. Once you have covered your school in English, try approaching your local library or community center.  Given the possible benefit to your students, I doubt you’ll experience any objections.