The Frankfurt Book Fair recommends using the public transport system to get to the exhibition grounds. This will help protect the environment and your nerves.
Getting from the central station to the Fair by public transport or on foot:
From the central station you can take the S-Bahn (commuter train), U-Bahn (metro) and Tram to the exhibition site. You can take one of four different S-Bahn trains to the "Messe" station (entrance "Torhaus").
The underground will take you to the "City" entrance of the Fair (stop "Festhalle/Messe") in less than 5 minutes (take the U4 direction "Bockenheimer Warte"). You can also take tram 16 (direction "Ginnheim") or 17 (direction "Rebstockbad") to the Festhalle/Messe stop.
You need about 10 minutes to walk from the north side of the Frankfurt main train station to the exhibition site. Take "Düsseldorfer Straße" to reach "Friedrich-Ebert-Anlage" and from there just head for the "Messeturm" (pointed skyscraper in front of the exhibition site).