a lot of people are saying water, which I agree totally but I'd saying throwing water on your face works the best. could do it over the sink and just massage your forehead, close your eyes and just relax your head. had a headache last night and throwing water and massaging my head worked great :D
Before you try to treat your headache, you should consider what might be causing it. Headaches can be caused by many things, such as dehydration, stress, fatigue, low blood sugar, intense light or sound, allergies, a bump on the head and so on.
Water is often helpful but if you haven't eaten recently, a glass of chocolate milk might be a better choice because the carbohydrates will give your blood sugar an immediate lift while the protein helps to keep your blood sugar stable.
Food sensitivities are common and often express themselves through headaches. If you seem to be getting headaches frequently, you could keep a daily journal of your diet, activities and moods for two weeks. Each day, make note of whether you had a headache, when you had it and what was happening around that time. Identifying headache triggers is an important step in preventing them.
I have headaches for over 5 years, and recently I have tried giving up eating wheat and I haven't had a headache since. Many people are allergic to wheat or gluten. It may be hard but it is totally worth it. I haven't had a headache in 2 months; its awesome!