Smartphone with google translate should help you with most situations, but be quick and familiar with it! Rent a sim card/data plan for Google maps (or your preferred alternative). Don't be shy about asking for help. Subway staff, police officers, etc. Do master the simple basics such as Where is X, This please, etc. There are restaurants that will not have an English menu and your translation app may or may not work, however many restaurants will have displays of food with prices, and you can take a photo and simply show the photo! Shinagawa is more international, and thus you'll find more English speakers, but don't limit yourself to that Ward.
Your question was specific to Japanese language barrier, but one external suggestion: August is pretty miserable in Tokyo unless you're acclimatized to hot and humid environments, try to avoid that month.