There are Currently 3 methods available for traveling from Narita Airport to Maebashi Station() :JR trains, KEISEI trains, and Airport Buses. JR and KEISEI trains depart about every 30 minute; Airport Buses depart 10 times a day. The 3hours 30minutes Airport bus ride, which does not require a vehicle change, is the most reasonable-priced and easy to use.
Tokyo Narita Airport official web site

JR Trains
The JR Line "Narita Express" departs both Airport Terminals from B2F platform. Ticket direct to Maebashi may be purchased at the B1F JR Tickets Window, or at the View Plaza Center opposite.

KEISEI Trains
The KEISEI Line "Skyliner" departs both Airport Terminals from the B2F platform.Tickets to KEISEI Ueno Station() may be purchased at the B1F Skyliner Ticket Office.

Airport Bus
The Airport Bus bound for Maebashi "Azalea Express" departs from the street-level Bus Stop() just outside the 1F Arrival Lobby of both terminals. At terminal 1 this is platform #5 at Terminal 2 this is Platform #10. Tickets for the Airport Bus direct to Maebashi may be purchased at the KEISEI Bus Information Counter, on the 1F Arrival Lobby, at both Terminal 1 and 2. Departure times at the Narita Airport are: 8:55, 11:20, 13:20, 14:50, 15:25, 16:10, 17:10, 18:00, 19:15, 20:30(Schedules are subject to change).
Azalea Express Timetable

Note:1F=Street Level
B1F=Basement Level1
B2F=)Basement Leve2