1) Improve The Melody
Play the melody by itself, on an instrument.  Play it very slowly.  Listen to it without chords or lyrics.  Does your melody tell a story of its own (without the words)?

Is it too static; does it need more motion?  Does it jump around too much (much less common!)?

Does it cover enough range, top note to bottom?  Or does it cover too wide of a range, making it hard to sing?

2) The Title
Is it a strong, evocative idea, at least to you?  Is there a way to say it that’s more colorful, catchy, interesting, memorable?

Does it come at the place in the melody where it ‘has to be’?  Usually the first and/or last line of the Chorus or, if it’s an AABA song, the first and/or last line of the ‘A”section, are the most effective places for the Title.  If yours is somewhere else, is there good reason?  Is it working?  (If so, fine… leave it!)

3) Experiment With The Bass Notes and Chords
Does the harmony support the feeling and meaning of the melody and lyric?  To convey that, is the chord progression too complicated?  Or is the chord progression simpler than it needs to be?

Try playing just the bass notes with the melody and see if that feels right – it’s the foundation of the harmony.  Are the bass notes you have the best fit with the melody?  Try some different ones and, if they’re better, start there – and build the chords on top of them.

This is a good place to remember Albert Einstein’s words: ‘Things should be made as simple as possible… but no simpler.’

4) Make Sure There’s a Groove – a Strong One!
Does the song have a powerful rhythmic  feel?  If it doesn’t yet, try it at different tempos, with different grooves.  Don’t be afraid to use the feel of another song you like, if your song is a good match.  A strong groove running through and under a song is a major asset.

One other thing – most songs sound best when they’re played all the way through at the same tempo.

5) Add a Counter-Melody and/or a Riff
Fool around with riffs and counter-melodies.

An instrumental riff can be a song’s signature.  A (counter-) melody line that can be played during or after the Chorus, and that compliments it, can really help punch up the Title line and make the whole song better.