I've discovered an interesting trick to increase motivation for composing, though it only works if you tend to listen to your previous work a fair amount. Myself, I listen to what I'm currently working on when I wake up and before I go to bed, as well as other random times throughout the day, even if I don't plan on composing at the time. That way, my current work is always on my mind at some level, and I find that it makes problems a little easier to solve when I finally do sit down to write. I often find it difficult to begin a writing session, even though I do fine once I've actually stopped procrastinating and begun.

The trick is this: At the end of a composing session, add a measure or two wherever you've stopped. Make it the most musically deficient, incredibly stupid music you can think of; trite music that you would be ashamed of in a public setting. Then every time you listen to it, you'll be so embarassed at its ineptitude that you'll want to drop everything and change it. Making that change will put you in the mood to write, and get the ball rolling. It's worked well for me this week.

"The good composer is slowly discovered; the bad composer is slowly found out." - Ernest Newman