From Shibuya Station, take the Hachiko Exit which leads directly outside Shibuya Crossing.
From Shinjuku Station to Shibuya Station:
Take the Yamanote Line direct to Shibuya Station (11 minutes, ¥160)
From Tokyo Station to Shibuya Station:
Take the Yamanote Line direct to Shibuya Station (24 minutes, ¥200)