Agree with jousis that the big name places only take reservations 2 months in advance and often require a concierge to contact them unless you speak Japanese, but many of the 1 and 2 Michelin star restaurants are surprisingly easy to get a table during the week perhaps because there are simply so many...

Tabelog is another good resource used by the locals, which often seems to include value for money into the overall rating. Google translate is your friend.