While textbooks, conversation partners, and flashcards are all effective ways to improve, has the thought of spiritual support ever come to mind?!
From Shibuya, take the Den-en-toshi Line to Sangenjyaya. Then take the Setagaya Line, which has a more local flavor, to Shoinjinjyamae Station. Exit Shoinjinjyamae Station and take a left. Go straight until you see Shoinjinjya.
Shoinjinjya is named after Shoin-sensei who was teacher and scholar from around the end of the Edo era. The shrine itself is made of wood and is fragrant and atmospheric. His classroom (juku) still exists on the site and is sure to scholastically inspire!