YY said wrote "the person who has an urgent message to communicate is less likely to be a great writer than the person who simply likes to play with words."
Ain't that the truth.
In the words of another poet (Muriel Rukeyser) "Keep your word-hoard dry". Cultivate a large, diverse, and polyglot vocabulary, then use it very, very, very judiciously.
Also,
If you can make the form (i.e. rhyme and rhythm) reflect content, you'll strengthen your lyric/song structure. E.g. songs about chaos are more powerfully chaotic if their rhymes and rhythms are disruptive; songs that tell stories are more easily followed if they have rhymes and rhythms that repeat and progress in a logical fashion.