I play the drums in a band with my friend and he plays guitar and sings. As far as lyrics go, what we always do is improv jam and see what we come up with. Then he'll navigate the music and hum melodies which eventually turn into words. For us, the music always comes first. I've been writing some lyrics on my own while I play guitar, again with this, I begin with chords and notes until I get a basic feel down. I'll let that inspire the lyrics and then I'll write them down.