I have used Narita Terminal 1 first floor (arrival) lockers in the central annex. They are tucked in behind the escalators and near the elevators. Working from memory, the steps go like:

1. Touch English on the screen
2. Touch Deposit Bag icon on the screen
3. Touch one of the available lockers on the screen, and the light on the door will flash
4. Place your bag in the locker and close the door which will lock
5. Return to the console and touch your desired form of payment
6. If IC card (i.e. Suica), touch your IC card to the reader. Your card becomes the key to unlock the locker. It will deduct the first day's fee from your balance. Take the receipt from the machine.
7. If cash, enter a PIN code and insert money (1000 bill, 500 coin or 100 coin) into the slot to pay for the first day. The machine will print a receipt with the PIN code on it (I think.)

When you are ready to retrieve your bag

1. Touch English on the screen
2. Touch retrieve bag
3. Touch your IC card to the reader or enter your PIN code. If balance is due, it is deducted from your IC card or deposit money to pay.
4. The door will unlock and retrieve your bag