Whenever I listen to songs from a young songwriter there seems to be a number of common problems that pop up, so here's a checklist that you can use before you deem your song finished. Regardless of how long you've been writing songs, these items can be useful, especially if you intend for your songs to be as commercial as possible.
1. Are the sections too long? Sections of a song that are too long cause the listener to rapidly loose interest.
2. Is there a clear distinction between sections? For instance, can you tell the difference between the verse and the chorus? Once again, listener interest wanes if a song goes too long without something new happening.
3. Does the song have a bridge? A bridge adds tension and release, keeping the interest high and enabling the song to build to a peak.
4. Does the song have a hook or identifiable riff? A strong hook or riff develops listener interest.
5. Does the song have dynamics? Dynamics (places in the song that are more and less intense) develops listener interest.
6. Does the song have a tight arrangement? See my previous post on arrangements.
There's a lot more information in chapter 9 of my band improvement book How To Make Your Band Sound Great.