Highest pitch in a Melody
One common property of many successful melodies is that the highest (and lowest) note of it only occurs once in the melody. This is a pretty essential thing in order to give it a proper dramaturgy. Also, the highest note shouldn’t be a function in the chord that wants to resolve upwards (e.g. the major 7th of the chord). Of course there are melodies that also work without following that but quite a lot of popular melodies follow that structural property.