Some considerations when writing about the first performance of a musical work:
Use Naxos CD booklets as a possible source of information
Oxford Music Online (Grove)'s main article for the composer may have information such as instrumentation and various arrangements of the piece of music, as well as narrative information about the premiere or the audience's reception of the piece
Use the ML410 section of the library to find books about the composer and their music
Newspapers printed the week of the premiere may also include reviews, which are primary sources
Don't forget to look at the context of society. What was going on in the world that could affect what listeners thought of the music? What aspects of art history, fashion history, political history, etc. might have shaped the composing or the setting of the music?