Play the notes that are in your melody line on a piano or keyboard when you are trying to learn them. If you don't know how to play them, ask a pianist to do this for you. The first couple of times, simply listen to the pitches.
Hum along as you play or hear the pitches on the keyboard or piano. Don't worry about lyrics just yet. Focus on the notes themselves.
Hum the notes without the help of the piano or keyboard.
Add the lyrics when you can successfully repeat the notes by humming.
Visualize the movement of the notes as you sing. You don't even have to know the name of each note. Just try to "see" in your mind how the notes move up or down on the paper.
Record yourself. When you listen to the recording, compare your pitch to the pitches played on the piano. Work on any areas that are giving you trouble.
Maintain erect posture and use the muscles in your abdomen to support your tone as you sing. As you sing, visualize your airflow coming from the area just below the center of your ribs.Gently contract these muscles as you push air outward during singing.