If you get the flu, you can do things to ease the symptoms. Do not let yourself get dehydrated. Drink plenty of water and other fluids. The fluids will thin all of the nasal secretions. Warm water mixed with lemon and honey is good to loosen phlegm.
Chicken soup works wonders for easing flu symptoms.
Keep the humidity at a higher level when you start getting flu symptoms. You can do this by using a humidifier or just by staying in a warm shower or bath for a longer period of time. High humidity will ease a sore throat and also loosen phlegm. If you do not loosen secretions and phlegm you will be more susceptible to getting bronchitis or pneumonia. To soothe a sore throat you can gargle with some warm salt water.