What is the best way to self-diagnose headache triggers?

Pay attention...: ...To little things, like time of onset, activity, lighting, recent food/drink intake, any meds, any stress/anxiety, time of month, ambient temperature (if high or low). These are just some triggers, but you get the idea--a "headache diary" often helps, and pre-fab one can be googled to reduce effort. After several days' data, look for patterns & show your dr.

Keep a log: Each time a headache happens, log the previous 48 hours: food, sleep, medications, activities, schedule, work, etc etc. More detail is better, and written logs are necessary--memory is too untrustworthy. Over time you may see comon patterns emerge--those are the likely triggers. Eliminate them and you may eliminate your headaches.