What process do you go through in writing a song?
Usually for me the song starts with a snatch of melody and a key phrase. It may be only one or two lines, or less. The way that little bit of melody and the text fit together portray the way I felt at the time. Usually if I sing the melody in my head for very long then I start getting cool harmony ideas. If something sounds like some other song I know, then I usually throw it out.

At this point I will get on the computer with two windows open: one for composing the music and a text editor for doing the lyrics, if there are any. I try to get as much of the melody and harmonies done as possible, and sometimes the lyrics just fall into place along with that. Usually I write the melody first and then the bass line comes pretty easy. After that I just fill in the middle parts and try to give them some interesting rhythms that are varied from the rhythm of the melody.

Then I usually write freestyle to express all the connected feelings I'm having. Sometimes a natural rhyme will come out of this process; sometimes not. But I don't force it at that point or worry about meter.

After I get the feelings all out in freestyle, I will go back through and try to organize them in logical sequence and try to put some more rhymes together. I am not a stickler for every line has to rhyme, but it really bugs me when songs act like they're going to rhyme, but then don't.

All in all, it's a lot of jumping back and forth to follow various ideas as they come.

Drums/percussion are usually the very last thing that I add. I hear the beat in my head anyway, so it's not really important to me to get it notated right away. If I decide that other people need to hear the beat as well, then I'll add a drum track. My percussion is nothing to write home about; I usually write a simple 2 or 4 bar pattern and repeat it throughout the song, with variations as needed for emphasis.