What I stated before has been quoted out of context. Lyrics, like the music itself, can either be composed along with the music, or separate from it, like a poem(s). I'm not saying that lyrics are not important. They are. However, a complete song on guitar doesn't necessarily need lyrics. Classical music or guitar is a great example. Even in modern music, instrumentals are not totally unheard of ... Classical Gas, comes to mind, and I'm positive there are thousands of others that I'm not aware of. At any rate, pop music has lyrics and so does most anything on the radio - cool whatever. But, songwriting has to start somewhere.

I think the main thing in songwriting is LISTENING. LISTEN to your chord changes, how they are played, the tempo, etc. and that sometimes will dictate what mood is coming across and, therefore, what lyrics should be and sound like. You also gotta remember who you are writing for: to please yourself, a certain type of music, pop music, or whatever. Some songs will lend themselves more naturally to certain styles of music. Other songs, on the other hand, may be different and lean towards a different style of music.

If you like composing songs on guitar, start with the guitar. If you wanna write lyrics also, then do so as well. Whether they are done together at the same time or not, many times the tempo of the song and chord changes will dicatate the melody and lyrics. And, above all, keep it simple. Some of the best, most enduring songs are simple and tight in structure with simple lyrics and melody. It's not rocket science. It's creativity. Know the rules and then play with them to create what you want.