Firstly, its not a good idea to title a song before you write it because you're just limiting yourself.
Idea wise you need to decide what sort of message & atmosphere the song is going to give off (Optimistic, Sad, Bitter, Crazy etc.). Then you need to decide the song's structure such as Verse, Bridge, Chorus, Verse...etc.
I tend to think of the music last because it just confuses me to think of it at the same time as the lyrics & structure.
If you're really struggling, use the structure of an existing song and fill in the lyrics as you wish to convey your message/emotion and change the title appropriately.