I did French Community Radio a few times. Keeping a playlist is a very good idea. Also, really try and plan out what you are going to do. Time constrictions and swearing can cause problems, but it will help if you have a good idea of what you are going to play when you get in there.
And saying stuff between songs. Think about what you are going to say, because otherwise you might just start mumbling something about a David Bowie instrumental in a very low voice before it goes off into Kraftwerk.
Finally, don't let the listeners get you down. If they don't like "Alluminum" by the White Stripes or any Serge Gainsbourg song, screw 'em.
Good luck.