Learn how to read the treble and bass clefs. Since music charts feature all instruments, both clefs will be used. It's a good idea to keep a reference for both clefs on hand. You can purchase one from a local music store or find one online free.
Study the conductor's score to see how all the instruments in the chart work together, which instruments are handling the bass and rhythm parts and which instruments are handling the melody lines. You want to have an idea how the instruments are distributed.
Study the individual sheets and familiarize yourself with the instruments in the score. Many of the instruments will look the same on a musical staff because they play in the same range, so familiarizing yourself with the instruments will help you understand the charts better. Each instrument should have the instrument name written at the top of the individual sheets.