Memorize the names of musical intervals: minor second, major second, minor third, major third, perfect fourth, tritone, perfect fifth, minor sixth, major sixth, minor seventh, major seventh and the octave. Purchase a music theory text to help you learn about chords if you need one.
Have a friend play two notes on the keyboard and ask you to identify the interval played. Repeat until you can correctly identify all of the intervals.
Play major, minor, augmented and diminished chords so that when you hear them, you can instantly identify them in a harmony. Have a friend play each chord until you can correctly identify the chord qualities.
Purchase a book of melodies that progressively get more complex. Listen to each melody as a friend plays it for you on the piano and attempt to notate it. You can copy the notes into a music notation program and create a CD of all of the melodies, or purchase a text that has examples for you to dictate.
Listen to recordings of duets. Notate the bottom melody first and then notate the top melody. Then listen to trios and attempt to notate those. Continue until you are notating complete four-part harmony.