Learn the names of the notes. There are seven note names in modern music that are the same as the first seven letters of the alphabet: A, B, C, D, E, F, G. Once you go all the way through the letters, you begin again with the first letter, now played one "octave" higher. Notes can also be "sharp" (indicated by the "#" symbol), making them a half-step higher in pitch, or "flat" (indicated by a symbol that looks like a lowercase "b"), making them a half-step lower in pitch.
Learn the names of the clefs, sets of five parallel lines that indicate the pitch of each musical note. There are two different clefs in each piece of music; the top clef is called the "treble clef" and the bottom is known as the "bass clef." The melody is played on the treble clef, and the bass clef is mostly reserved for instruments and the vocal bass part.
Learn the notes on the treble clef. Notice that there are five lines and four empty spaces between them on each clef. The notes on the lines of the treble clef in ascending order are: EGBDF. Remember this by the phrase, "Every Good Boy Deserves Fudge." The notes within the spaces in ascending order are: FACE.
Learn the notes on the bass clef. The notes on the lines in ascending order are: GBDFA. Remember it by the phrase, "Good Boys Deserve Fudge Always." Notes within the spaces in ascending order are: ACEG. Remember it by saying, "All Cows Eat Grass."
Figure out the key. All music is written in a particular key. Written music will tell you which key to play right at the beginning of the piece. You will find the key written next to the treble clef; if there is nothing next to the clef, then the key is in standard C. Other keys will be indicated by sharp and flat symbols on a line or space corresponding to a note; if note has a flat or sharp in the key, you default to playing that note a half-step lower or higher, respectively.
Find the time signature. The time signature is indicated by a fraction number with the numerator telling you how many beats are in each measure and the denominator tells you which note gets one beat. 4/4 time is the most common time signature, for instance. It means that a quarter note (denominator) is worth one beat and that there are four beats per measure (numerator).