One of my triggers, and I have heard others say this is a trigger to them, is flickering lights. It can be anything such as light through branches of a tree that is blowing in the wind; light flickering on water; fast changing. images on TV or a movie screen. I make a practice, if I am able to, to close my eyes and get away from the flickering light.
My daughter has a trigger I had never heard of before. Rain hitting on dry soil always makes her have a migraine. She says it's the smell that causes it.