J.,
Migraines are spasms in the blood vessels in your brain. They are caused by a hypersensitivity to the constriction and relaxation of blood vessels. Many things we eat, such as caffeine, cause our blood vessels to constrict (vasoconstrictors). Other things, such as foods with polyphenols such as wine, chocolate, and berries, cause our blood vessels to relax (vasorelaxers). For some people, too much of this constricting and relaxing will cause a spasm. While you are having the aura, that is the actual spasm. And as you know, the pain quickly follows. The first thing you can do is identify and limit how much of these foods you eat. Here's an article that lists some of the foods to limit: http://familydoctor.org/127.xml Cutting down on caffeine can especially help. Although, once you have a migraine, medecines like Excedrin Migraine actually have caffeine in them because that can help the pain once a migraine has started.
Many studies have shown that certain vitamins can stabilize your blood vessels to prevent all this relaxing and constricting and greatly reduce the frequency and severity of migraines. Riboflavin (which is vitamin B12) and magnesium are two that are available in health food stores and are completely safe to take, up to 400mg/day if you want. Feverfew is another herbal supplement that seems to help but that is not recommended if you are pregnant or nursing. My husband and I both take riboflavin and magnesium every day to prevent migraines and it has helped tremendously.
Here's a great article from the American Council for Headache Education:
http://www.achenet.org/articles/45.php
Good luck!
S. T.