Notice the shape
Try humming a melody without the lyrics. Listen to where it rises, falls or stays on a repeated note. A short, simple phrase can become memorable when its shape is clear.
Listen for repetition and surprise
A repeated phrase gives your ear something familiar. A changed ending or a higher note can create contrast. Pay attention to how much a song repeats before introducing something new.
Match the melody to the feeling
Sing the same words slowly and then with more movement. Notice how the mood changes. The best choice for your song depends on the feeling you want to carry, not simply the number of notes you can sing.