Stress is #1. Ironically it isn't when I'm under the stress. I will get a migraine once the stress is finally off.
Hormone changes - first day of my monthly cycle. I used to get a hellacious migraine on that day until my doctor made some changes.
Changes in sleep patterns. If I have a restless night of sleep or, on the flip side, sleep too long.
Alcohol - it pains me. I love beer, but beer does not love my head.
It's no fun being a migraine sufferer. 32 years of dark rooms with ice packs and quiet surroundings.