I've had them for almost 30 years, I really don't know the triggers either. I started keeping a log, but that only served to tell me how often I was having them. Sometimes I would get a couple per week, other times go 6 months without one. I will tell you this, however. In January 2013 I radically changed my diet. No sugar, no gluten, no dairy. (After 5 months I added back fruit.) In the time period from Dec 2012 to now I've had one migraine, occurring in May 2013. I'm not sure what to think, other than once I went off the deep end with my diet, things changed. Also, my seasonal allergies, which usually pushed me to get prescription meds each spring and summer, almost completely disappeared. The doctor that suggested these diet changes said it's probably due to an underlying allergy to 'something,' and in my case most likely dairy. Once I quit the dairy, my body just seemed to settle down.
Keep in mind that I've had breaks in my migraine occurrences before, but this time I'm somewhat hopeful I've found a real key to the puzzle.