pretty easy, because

There are always Chinese characters showing you where you go, where yo take bus/taxi. Plus the Japanese persons are quite nice to tell you althrough it s a bit hard for them to talk in English.

After getting out of the airport, pls first to gonna the information centre to ask how to buy ticket for Yokohama. I am pretty sure there must be heaps buses heading every city near Narita. Or take Narita express, I have no idea about it as it is pretty new.

BTW, I will go to Japan on 22nd of Feb. Good luck for your trip.

Cheers