OK....The way it works for me....is that I'll be strumming a chord, maybe two...but that's all....and I'll hear the first couple parts of a melody over those chords....At this point I STOP strumming chords....And I begin to figure out what the notes of the melody are before continuing onward.....Once I have done that, the next step is trying to figure out what the remainder of the chord progression is (remember only started with one/two chords) Sometimes the first two chords and maybe a third one is enough to satisfy the entire melody..
Other times I have to search the guitar/piano to find more of the right chords to fill the space behind the remainder of the melody... It's as if I know exactly what the chords are I'm searching for and as I continue to strum through all the different chords inorder to find the right ones, I'm hearing the right ones in my head...and I know that as soon as I strum them I'll be like BINGO...that's the one.... However, I also know my music theory so I am able to minimize the amount of chords that I actually have to search through...given a particular note in a song, it can usually only be a couple of different chords that could operate with that note....at least in terms of the key that the song is in..
Once that's all done...then I have the structure of the song...However, I am like a mad scientist when I'm writing songs, so I continue to experiment...Doing thing like Chris does with Harmonies and yes, occasionally doing the exact same thing as he does; changing the harmony part to the lead part...I do this not necessarily because one sounds better than the other, but because one normally sounds better when I'm the one singing...I always try to do what is best in terms of the limitations of my voice. And making the harmony part the lead part normally doesn't typically affect the feel of the song that much anyhow...
Like Chris, sometimes I also try the melodies over different chords, i.e. "relative majors and minors" are a good place to start for this method.....
Despite all this, I usually wind up sticking to my original formula.........Because otherwise I just start to confuse my self with my stupid mad scientist way of songwriting
Good question though, I'm going to use my psychic ability right now: Sick drummer, there will be alot of different answers and opinions to this question....
- nave