Yes, I'm working on this.
In college I had taken some theory classes, but I didn't own any melodic instruments to apply them to, and then I got so busy playing drums in bands, it all went out the window.
Then a few years ago, I had formed a new band, and we were working on an album, but we couldn't find a guitar player that gelled with what we were doing. I had a guitar that I had picked up cheap along the way, so I figured out just enough to record some songs. And then started on keyboard parts. I ended up writing a song for the band all on my own, and my band was impressed enough to actually record it.
Go to
http://www.myspace.com/drumeatdrummusic, the 3rd song down "Ashes to Earth" I programmed all the keyboards, I played all the electric guitar parts (not the acoustic), and wrote the lyrics, and base line (which my bass played then expanded on).
My problem is I'm not exactly sure how I came up with all the parts. It started a 4 bar loop, and sat around forever. Then suddenly, one day I sat down and the whole song just poured out of me.
With keyboards, you really don't have to learn how to play, because you can use midi to program anything, which is what I do. So it's a long process, because I literally program all my keyboard parts one note at a time.
The 1st two songs on my myspace page I also wrote all myself. They're very prog.
"Searching" needs to be re-mixed to sound better, and I need to smoother out some transitions, but I'm on everything. A buddy helped me figure out some of the bass lines in the 1st two sections, but I programed or played everything else. It took me days to program out the piano solo at the end, because I did it one note at a time.
It started with the weird syncopated drum part over a piano part in my head, and somehow expanded from there.
The first song "Into the Mist" is also completely written by me. I played everything, but then a kid I know who's a wonderful guitar player re-recorded my guitar parts so they sounded more "guitar like" (and he came up with the actual solo) and another friend re-recorded the bass line so it sounded less stiff. This song took about a year from when I laid down the 1st note until I was done.
Hopefully, one day I can have someone add vocals to both songs.
It's long frustrating process, because I am a drummer 1st, and other instruments are near foreign languages to me. I'm doing it all based on some theory class I took over ten years ago that I can barely remember being in.
On the positive side, technology helps so much. Using midi makes so much of it easier. I can download midi versions of various songs and see how they formed the chords, and the relationship between chords they used to make a progression. And then using midi, I can program my own chords and changes one note at a time without having to play them on a proper keyboard. For guitar, there are 101 websites out there that will show you the fingering for common chords and various songs.
Youtube is full of basic lessons for different instruments and different styles.
And like any musician, I take songs I'm really into and break them down for inspiration.
FOr example, once the 1st riff is played, does he go up or down in pitch for the next part? Is it a big change or a subtle change? Are the other instruments playing the same part, or are they playing something differently that works with the 1st part?
And from there, it's a lot of trial and error until something works.
I wish I could go back and re-take a harmony and theory class, and maybe some day I will. But with two small kids at home, I don't really have the time right now.