I suffer from migraine and use "Migralieve" http://www.migraleve.co.uk/tips.aspx
Dehydration can be a strong trigger so it is important to drink water regularly, also avoiding strong cheese, Chocolate and smoked meat products.
I found that keeping a diary of what food and drink I had, and also other aspects of daily life such as sleep/tiredness and stress helped identify some triggers, the main ones were stress and irregular sleep. The first signs I get of an oncoming migraine are aching behind my left eye, sweaty neck and heavy yawning, usually drinking a pint of water and taking one pink migralieve will stop the onset.
However, it is important to see the doctor as severe headaches can be the sign of other problems!