The correct ratio of sugar to water for hummingbirds should be 1 part sugar to 4 parts water. You should boil the mixture until it completely dissolved the sugar and let it cool before putting it in clean, air-dried feeders.  Avoid using brown sugar or honey instead. Use white cane sugar only. Avoid red dye like the plague, as it could harm the little critters. Change the nectar twice a week or when you notice it is turning milky or cloudy, and clean the feeders thoroughly before refilling. Keep extra sugar water in the fridge for two weeks to ensure you serve only fresh, nutritious food.