Most of the time I compose by first writing a melody, or at least a melodic figure. Sometimes I compose by first writing a chord progression. That is what I did when I composed Willow:
The chord progression is: C, G, Am, Em, F, C, Dm, G. This than repeats 4 more times beginning at :27,:48, 1:02, and 1:18. What I do is play the chord differently each time through (called a Variation). For example, the progression begins with a C chord. Here is an example of the C chord beginning each time through the chord progression (click on image to make bigger):
It’s still a C chord (C Chord= C, E, and G), but each one is a little different. I used the same technique in my arrangement of House of the Rising Sun.
The chord progression is: Am, C, D, F, Am, C, E, E, Am, C, D, F, Am, E, Am, E. It starts at 0:15. Each time through I make changes (variations). The first variation (0:39) I play the melody and chords in an upper register (higher). Second variation (1:00) I play faster (triplets). Third variation (1:20) faster yet (16th notes). Final variation (1:41) strumming.
scores, tabs, mp3s available at http://www.robertlunncomposer.com