After getting to the airport, you'll need to go pick up your JR Pass (should be included with your ticket). If your flight comes in too late (and the ticket place is closed) I'd recommend shelling out the $30 or so to go into Tokyo without the JR Pass and get it the next day in the city.
Once you've gotten your ticket, hop on the JR Narita Express (NEX) to Tokyo. When you get to Tokyo, check into wherever you're staying and scope things out. It's probably evening by now anyways, so do your best to unjetlag yourself and go to bed so you can wake up early.