I recently had e-mail from a new, young (14!) songwriter who wanted to know how to come up with the music for her lyrics. Since I usually come from the opposite direction (i.e. I usually come up with music first), it made me think about approaching it from the lyrics first perspective. I sat down and wrote out some lyrics off the top of my head and then realized that I definitely had a rhythm going while I was doing it. Not necessarily a melody, but since I usually write to an established meter with the music already created, I think this brought out my instinct to automatically meter the words.
The difficulty was in developing a melody to them. Elton John is someone who has always taken that role, receiving the lyrics from Bernie Taupin and putting a melody to them. In an interview I saw with him, he discussed how he first reads through the words to get a feel for the "mood" of the song. Sometimes he will change things around (I guess Bernie gives him some artistic license!), making a verse into a chorus or the other way around, adding or changing lines slightly to accomodate what comes to him musically.
Don't be afraid to let the melody do the "talking"...if the melody starts to write itself a little differently compared to the lyrics, go with it. I heard once that a sculptor looks at the work as already existing within the material...his/her only job is to remove the unwanted stuff. I think you can remove or add lyrics or adjust your meter to make it fit the music and still remain true to the essence of the song.
How to come up with a melody? I once had to write the music to a whole bunch of poems in the play "Through The Looking Glass" (realizing much later that this had already been done professionally!) in high school. This was quite a challenge for me and I worked up quite a sweat doing it! Instead of trying to come up with chords, I "sang" the words...I just repeated them and sung a melody off the top of my head until it developed into something tangible. Then I sat down with the guitar until the chord "sounds" in my head matched the melody. It took alot of patience (when doesn't it?), and it gave me a whole new outlook into songwriting! Needless to say, I went back to songwriting in my usual way!
Recently a student came to me with a melody she had in her head, but she wasn't good enough at playing the guitar to play what she "heard" chord-wise. She hummed and I tried all the chords I could come up with and it was pretty frustrating! In the end we still didn't find it, but she learned more about how to experiment on the guitar until she could come up with it herself!
Coming up with a melody first is my "specialty". I usually do this by sitting down and experimenting with chord progressions, but sometimes I'm in the strangest places when the thing hits me! Baths are great, so is a walk on a beach for me. Driving the car with no radio or tapedeck playing is good too. What also works for me is learning a new song by someone else...lately Shawn Colvin's "Sunny Came Home" has been a source of inspiration...the rhythm of her writing is really catchy and the progressions in that song are terrific. I don't copy it, of course! But when I learn something new, it often brings out something new because the mood of it can inspire. Or I play it wrong and come up with something else!
There are many schools of thought in terms of writing...my writing is very instinctive and never comes from a "well, this is a 'C' so I should be using an 'Am' " attitude. But I have come across a number of songwriters who do exactly that...they come from the theory end of it. In fact alot of serious songwriters study the theory end of music quite voraciously, looking for a clue to writing a 'hit'. There are all kinds of theories about hit songwriting. For me, I focus first on coming up with something that pleases my ear, and then I worry about whether or not anyone else will like it! Que sera, sera!