Decide what voice part you are. If you naturally sing high, you are either a soprano (for women), or tenor (for men). If you sing low, you are an alto (for women) or bass (for men).
Find the line for your voice part. The lines for parts proceed as follows (starting at the top of the page): soprano, alto, tenor, bass.
Follow the notes. Notes that go up on the staff will go up in pitch as well. Notes that go down go down in pitch. The bigger space between the notes, the longer the interval to be sung between the notes. Different notes will be sung for different amounts of time. The more "tails" a note has, the faster it will be sung. "Hollow" notes will be sung for a longer time than a filled in note.
Follow the words. The words to be sung are generally right below the note they correspond to. If there is a line after a word, that word is to be held out until the line ends.
Pencil in any notes about pronunciation, breathing or anything else about singing the song that may be told to you by your conductor. This will help you remember them for the next time you sing the song.