Hello aragorn - The best way to start writing songs is to start with whatever you got to start with. If you've already got some melodies, then that is where you can start. Ideas for lyrics are all around you - just start writing about what you see or feel or think. Jot down lots of ideas and then let those ideas simmer while stirring gently. Keep a notebook with ideas and work in progress.
Have fun and keep it simple. Not everything you write will be a gem - most stuff will be gravel. Read the lyrics of songs you like and notice how the song is structured. The more you try to write songs the easier the process becomes - but there is no perfect system for creating a perfect song.
Remember that a song is just a few words and some notes put together. Have lots of ideas to play with - if one song idea is not working out it is not the end of the world. There are always more ideas to play with. James
"That darn Pythagorean Comma thing keeps messing me up!"
[url]http://en.wikipedia.org/wiki/Pythagorean_comma[/url]