I don't recall my brother's motivation, but he just decided he'd run a mile every day. He managed this for 370 days. Keep in mind we lived outside of Phoenix, Arizona, where it can be 100 degrees at 10 PM in the summer. But despite the rain or (more often) sun, he just did it.
I can't run a mile. I can kind of sort of jog a bit and then walk for a mile or two (and it HURTS!). I'm not even saying to write every day...but I know I need to have some sort of goal and dedication to work at it...that's the only way to have a chance. Just doing a little when it catches my fancy is not enough.
Better get back to work!