Before starting to getting started, how to read and pronounce Libre.fm ? :-) I think Libre is a french word meaning Free (as in "free" speaking, not "free" beer). And the "." dot between "Libre" and "fm" is called "point"(without prononcing the "t"). Or Libre.fm can be read in whatever way/language, since it's free :-) ? (someone should record the different pronounciations with a microphone in a .ogg file and put it here)
Come hang on IRC, discuss what you want to add -- irc.freenode.net #libre.fm
If you are using other people's code, make sure it is under a compatible license such as the Apache 2.0 license, BSD or X11/MIT license.
If you know a language besides English, you might want to consider helping with Translations.
The FSF holds the copyright to GNU FM so they can defend everyone's freedom to use it. This means that if you are making a non-trivial contribution of code to GNU FM you'll need to sign copyright assignment papers with the FSF. This article explains why, and this one explains the process .