I wouldn't call myself an expert on this subject (have been writing for 1.5 years only), and I guess this should be taken with a grain of salt. It's not a good idea to force these characteristics into songs; they (except for the fifth) are better off working their own way in.
I think much of this advice has to do with topical songs. It may not be as applicable to songs dealing with relationships.

1) A quotable line or central theme that you can build your song around. As old school as it sounds, a song is kind of like an essay. You need to have a claim, and the other details help support this. A line that might sound cliché to one person can be something that your audience remembers later on.

2) The connotations of words are important. Because a song needs to be relatively short, every word makes a point. I often find myself spending a long time deciding which words and phrases to use.

3) Poetic elements. Songs don't have to be super flowery, but some description and figurative language can help expand an argument beyond its logical basis.

4) Phrases that are also pleasing to the ear, can also make the words stick in the mind of the listener. I agree with what has been already said on this thread; that a songwriter needs to have an ear for how the words will sound together.

5) Experience. While political songs are hard to build from direct experience (in my opinion), careful observations of what goes on around you (in daily life, and not always just your song subject in the news) can provide the insight for a song.

Thanks for bothering to read this long, overly-analytical post.