Migraines are due to a sudden drop in blood sugar level in the brain. What exactly causes this drop, is something of a moot point.
Various "triggers" have been identified, all of which increase the chances of an attack. (Even if the trigger (for example, milk) is a definite cause in an individual, it doesn't mean that every single time that person drinks milk they will have a migraine. It just increases the chances.)
The following are generally recognised triggers, with a few I myself have discovered (being a Migraine sufferer):
Dairy products, particularly Cheese. (Chedder cheese is the worst.)*
Chocolate*.
Caffeine*.
Aspartame*. (A.K.A. E951) An artificial sweetener found in most soft drinks. This is a very understated, yet potent cause of Migraines. Check the ingredients label of any soft drink you buy - there are very few without this menace. Fanta Ice Lemon, Fruit Twist, and Asda High Juice are 3 of the ones which definitely don't have it.
Red Wine*.
Lack of sleep.
Too much sleep.
Bright/flickering lights. (Wear shades when out in the Sun, and avoid watching TV in the dark.)
Hunger.
* - The chances of having a Migraine from these triggers is exponentially multiplied if you consume these products on an empty stomach. Ergo, if you have them straight after a meal, you're less likely to suffer ill effects.
The method of relief I have found most effective is to crush 2 paracetomol tablets into a fine powder (this way, they are much quicker to digest), and drink them with a carbonated, sugary drink. (To combat the blood-sugar drop.)
THE MOST IMPORTANT THING when administering any form of digestible pain relief is to do so within 20 minutes of the first signs of a Migraine. After this, your body ceases digestion, and any tablets you take will be ineffective.
Once you've done this, hot-foot it to a darkened, cool room and try to sleep.
Generally speaking, if you follow this guide, you should be able to minimise the effect your migraine has, and resume what you were doing previously within 30-60 minutes, depending on the severity of the attack.
I cannot stress enough, though, that prevention is better than cure, and you should avoid ALL triggers if at all possible, as scientific tests have proven that every Migraine you have damages your brain slightly, and leaves you more susceptible to further attacks.
Digressing to the opening query:
My attacks began at around 11 years old, and peaked at I would say, 14/15. Then they declined in line with my identifying my own triggers, to where I now have them very infrequently, going months at a time without them, provided I stick to my own guide.
I hope this helps any fellow sufferers.