Play the middle C on a piano, and match your voice to it. On a standard 88-note piano, the middle C is the 40th key from the left. It is a black key, also known as an accidental key. On a standard tuned guitar, start with the C on the G-string. This note is at the fret.
Play descending notes on the piano by pressing each key to the left of the middle C. Match your voice to the note as you play it, and do not stop until you reach a note that wavers, breaks or audibly strains your voice.
Play the notes from the middle C down to the wavering note. Continue to work within that range by playing each note and matching it with your voice as you play the note. Do this for about 30 minutes each day. When you begin to feel more comfortable with the wavering note, go to the next lower note that makes your voice strain.