How early should i get to the airport?

ok so on the last day that im going to be in tokyo im going to Harajuku. My flight leaves at 6:50 pm. how early should i get the narita airport?

it is recommended to be at the airport 3 hours prior to departure (international flights).

The offical check in deadline at Narita airport is for all classes 60 minutes. But check with your airline if they ask for extra time because of class ( economy ) or destination. In general arrival 120 min prior flight time should do.

When I used the NEX to go to T-1 at NRT from Tokyo Station, I try to depart Tokyo Station no later than 2 3/4 hours before my flight departs.

The process of checking in and clearing immigration at Narita is very efficent

NRT isn't LHR or many of US airports, so getting there 2 hours prior to departure would be good enough, judging from my experience (70 times?).
Have never had any problem so far.

whether Yuliza is a male or a female:-) Shopping in duty free area of Narita airport is awesome, so be sure to have that extra hour if you need to buy some cosmetics, cakes, sake, tea and souvenirs ;-)

1530 should be a good time to arrive for a 1850 flight. It is best to arrive early at the airport to give yourself
time to get everything done when you are calm and not in a "I am late" rush. As of this year(2008) many airlines going to and from the U.S. may end their check-in at 1 hour before the flight departs so they may send in a list of the passengers that are on the flight to the U.S. government before the flight departs. Even if your flight is not going to the U.S. many airlines may still close the check-in at 1 hour before departure time. If you miss your flight, the next flight to where you are going maybe the next day, and if it is the busy season, there may not be a seat for you on that flight. It is always easy to kill a extra hour at the airport. I work at a airport and everyday see people who missed their flight because they wanted to spend another hour at the beach. And as "Flying Diva" suggested, do some shopping at NRT.