VM phrases
The soul of a melody is its rhythm. The "rhythm" of a melodic phrase is defined by where the notes fall against the underlying meter. Meter of course is defined by where the stressed and unstressed beats are. Like "simple meter" would be "ONE and TWO and THREE and FOUR and". Now, where your melodys notes are against those types of patterns are the earliest and most primal indications of how your melody is going to effect the listener. This is BEFORE the pitches are ever chosen. The melodic rhythm against the underlying musical meter is crucial to how your melody will work.
If your melody note lands on a stressed count (masculine), that is a strong note. It feels like the note belongs there. If your melody note lands on an unstressed count (feminine), its a little unpredictable sounding. Variations within these two rhythm "counts" are all there is (aside from grace-note like slurs and stuff like that). Either your notes are ON BEAT or OFF BEAT. Study your favorite songs and draw a little diagram depicting where the musical counts lie (stressed and unstressed) and the mark where the melody notes fall in accordance to those beats. Take notice of how good writers try to keep things interesting. Most times in great songs, you will find that they use as much contrast in how things are constructed as possible. Meaning a verse with many masculine melodic notes usually can use a feminine or two in key parts of the melody, or in adjacent parts of the song. Just experiment with what feels "good" and learn how the greats did it and you will start to get a feel for how to vary your own melodic rhythms in interesting ways.
Now, the next most important thing in melody after rhythm is melodic starting point. Meaning; "Where does the melody start with regard to the chord sequence?" There are only three variations which are before beat one of bar one, on beat one of bar one, and after beat one of bar one. There are no other ways to begin a melody, so choosing from those three is simply a matter of how you want to get creative and what feels best. Make a list of maybe like 5 of your favorite Beatles tunes or something and listen to when their melodies start in the verses and in the choruses and bridges. You will find that most great writers vary the melodic starting points from part to part to add variation and unpredictability to their songs. Remember there are only three starting points, so the variety comes in variations within the song itself.
(verse melody starts ON beat 1 of bar 1, then chorus starts BEFORE beat 1 of bar 1, then bridge surprises by starting a bit AFTER beat 1 of bar 1) just for example, there are many many different possibilities with different results, all stemming from those three. How to know what you prefer? Study the melodic starting points to all song parts of your favorite songs and try those techniques in your own songs.
Now as far as melody vs harmony (that means the chords you are playing) there are three speeds at which melody can move against harmony. Melody can move faster than harmony, slower than harmony, or at the same speed as harmony. Faster is the default and is most normal sounding. You know how it goes, you are singing a few notes for every chord change. The next variation is when melody moves slower than harmony. This is very exciting to the listener and has been done TO DEATH by both Radiohead and Coldplay. All you do is hold out notes while the chords change underneath. Its a dramatic effect and the audience will think you are some kind of genius and you will be rich like Radiohead and Coldplay. There are a million brilliant and potent variations within this trick that you should spend much of your time playing around with as practice. Find your own variations of this technique cause it takes average music and makes it sound above average. The last speed is melody moving at the same speed as harmony. This is a very bold and very noticable sounding trick that is rarely used. I personally have found that short spurts of this within a song works much much better than doing it all the time. It stands out. Its a high point in the song. You cant have all high points so use this one sparingly for just certain parts or the end of a chorus or bridge when you want to build up a release. Its what all the greats do so try to see if you can identify these three melody vs harmony speeds in your own favorite songs and try them yourself. Variations of the three within one song will go ten times farther than only one kind. Know when to change it up.
Seriously, knowing what variations there are and when to change things up are where the illusion of "talent" lies. All of these things i just talked about make up the element of music called "metric concordance"- how the melody falls against the beat and underlying meter.