I’ve done a little research and although I’m not a local, (far from it,) I have some info for the arrival from Narita airport to Yokohama. I’m more than happy to be corrected but here is what I have so far.
After arrival at Narita airport Tokyo, there are many options but by far the most cost effective and reliable is by Japan Railways (JR):
The fastest option to get to Yokohama is the JR Narita Express (NEX), requiring roughly 90 minutes for the one way journey. All seats are reserved. The one way fare between Narita Airport and Yokohama Station is around 4200 yen. (US$47, A$52, 32euro) There is about one connection per hour.
Also, from Tokyo station, JRs Keihin Tōhoku and Tōkaidō lines stop at Yokohama station (¥450, 40 minutes); some continue on to Sakuragichō, Kannai and Ishikawa-chō (all ¥540). The Tōkaidō shinkansen stops at Shin-Yokohama station, northwest of town, connected to the city centre by the Yokohama line.