Welcome to Japan! I recommend the Limousine Bus to come to Tokyo from the Narita Airport. Because it is easier than a train you must carry a luggage by yourself. It costs about 3,000 yen as same as a train. If you want a train, the Keisei skyliner is cheaper than the JR Narita Express.
If you have a time at the airport, Narita-san temple is nice to visit. Don't forget to get a map at the information center of airport before that! And then you can leave your luggage with some changes.