learn to read NOTAMS - airfield ones and FIR ones
TAFS/Metars as Maude Charlee says - you might wanna learn how to decipher graphic weather too - hig sig charts and winds aloft.
http://www.jeppesen.com/wlcs/index.j...nt=weather.jsp
you'll also need the patient and skill of a saint - if you're dealing with EuroControl (flight planning)
you may also be exposed to things like crew rostering, third-party service setups (eg fuel, handling, catering), you may assist with crew visas etc
get a good idea of what the job entails before you sign on the dotted line!
these sites may be of use....
www.dispatcher.org/
http://euro.wx.propilots.net/
Abdel