by Gary Ewer, from “The Essential Secrets of Songwriting” website:
Many songwriters start the writing process by coming up with a chord progression, and then try to create a melody that works with it. The problem with this approach can be that the melody lacks shape, as the importance is placed on the progression first. And a melody without a real shape becomes difficult for your audience to remember, and, quite frankly, boring.
One easy solution is to work on a melody first to which you add chords. In my experience, most songwriters find this to be a trickier way to write (though it can yield better results in the long term.) In any case, it’s important to remember this: while simplicity is an important characteristic of both a melody and a chord progression, a melody usually needs contour, while a chord progression simply needs to work.
Here are some standard signs that a melody will be boring to your listeners:
Problem #1: The melody is mostly stepwise (i.e., has no leaps). If your melody goes from note to note without leaping, it affects the potential energy of your song. A leap will inject energy into the melodic line, but be careful when you do it. A leap in a melody should coincide with an emotional word in the lyric.
Problem #2: The melody is too leapy. Too many leaps makes it difficult for a listener to remember the melody, and destroys shape. Smooth out those lines, and keep only the leaps that enhance the lyric.
Problem #3: There’s no real difference in the tessitura (basic range) vis à vis the verse and chorus. The contours of a chorus melody should take the voice higher than the verse.
Problem #4: There’s no recurring motif. A recurring motif is a short melodic idea (a hook is an one type of this) that occurs throughout your melody. In the Beatles’ Yesterday, that descending stepwise figure that happens on the word “yesterday” is a recurring motif. It helps glue the song together. Look for ways to incorporate a recurring motif into your melody.
Treat your melody with care. Remember, you’ve got to create something that will keep people humming all day if you want the song to sell. Your melody is your way of connecting to your listener, and a song with no real shape will die the death.