My way of handling lyrics is to not write them at all. I'm a decent writer when it comes to essays, but I absolutely suck at writing songs. I write songs with no words at all, or I hook up with other bands and just play guitar while they write words and sing. I can sing... made All State Choir, but I don't like to sing anymore, so I let someone else do it while I do what I like. As for which to write first, if you write both music and lyrics, just do what you're inspired to do. If you have some great words in your head, write them down and write music to it. If you come up with an outstanding riff/chord prog., then write words to go along with it. But remember, not all songs have to have words, and not all songs have to have music (and there's no order to which songs must be written). I like heavy, fast guitar when it comes to my musical tastes, but it's surprising how good some a capella choirs sound.
"You must stab him in the heart with the Bone Saber of Zumacalis... well, you could stab him in the head or the lungs, too... and the saber, it probably doesn't have to be bone, just anything sharp lying around the house... you could poke him with a pillow and kill him."
- Aqua Teen Hunger Force, The Universal Re-Monster