The CDC highly recommends vaccination against influenza. The inactivated vaccine is the most likely way of prevention. However, because influenza mutates so easily, the vaccine must be changed and readministered every year. One should receive the vaccine in the fall so that he or she has enough protection before the flu season starts. A minority of vaccine recipients experience arm soreness, and a very small minority develop fever and other flu symptoms. The CDC has more specific information on Vaccination. Medicare nows pays for the vaccine.
Other methods of prevention include chemoprophalaxis, using the antiviral agents of rimantadine and amantadine. However, vaccination is usually more effective, so this method should only be suggested if it is too late to receive a vaccination.
Of course, maintaining a healthy immune system, by getting plenty of rest, eating well, and exercising will help you prevent influenza infection.
In terms of worldwide prevention, an important factor is surveilance. The CDC asks that influenza be reported. It looks at the pathways of strains all over the world and then attempts to predict the strain of the next flu season for the best vaccine. Here is an article about how such predictions are made. As seen with the recent panic in Hong Kong, controlling infected animal populations is one way of trying to avoid human epidemics.