Here are some evidence-based protective measures you can take to help prevent infection:
1. Wash your hands
...then wash your hands some more. In fact, one of the studies examined in the relevant Cochrane Review showed that simply washing your hands at least 5 times a day cuts the risk of coming down with a respiratory infection by almost 50%.
Handwashing is one of the most important things you can do both to keep from getting the virus and to keep from spreading it, if you happen to be infected. --And it's important to understand that you may well be contagious for 24 hours before you show any symptoms. That's one of the reasons why influenza is so much harder to control than the SARS epidemic was.
Most people, even those who have the training to know better, don't wash their hands correctly. For instance, did you know that every time you wash your hands, it should take you 20-30 seconds to scrub them thoroughly (long enough to sing the alphabet song once or the "happy birthday" song twice)? For more on how to wash your hands correctly, see the CDC's video "Put Your Hands Together."
2. Stay away from infected people (and stay home if you're infected)
This is called "social distancing" and it sounds pretty obvious, but it's one of the hardest recommendations to stick to. That's because during a pandemic simply going to work, going out to buy groceries, going to a doctor's appointment or going to school could put you in contact with infected individuals or put others at risk if you're infected.
And, as I mentioned above, people (yourself included) can be contagious for 24 hours before showing any symptoms. When it comes to a flu pandemic, the fact that people feel well or look well is not a reliable measure of the risk they pose to others.
If this does become a pandemic, the safest thing you can do is stay home and avoid contact with others as much as possible.
3. Use personal protective equipment (PPE) when you might come into contact with infected individuals
There has been a lot of talk over the last few years about the use of N-95 particle respirators as a way of avoiding infection, and they have been shown to work pretty well when used correctly... but the Cochrane Review I mentioned earlier found that there was no statistically significant difference between their performance and that of simple surgical masks. Another study found that using nylons (AKA pantyhose) to hold the surgical mask tighter against your face improved their performance even further. This is a more foolproof form of protection than the N-95 mask, which must be correctly fitted and it may be more comfortable, as well, which has implications for compliance. --Paper masks were not shown to be effective.
Eye protection (in combination with masks) was also shown to be effective by the Cochrane Review. It's not clear whether this is primarily because goggles protected users from airborne droplets or because it prevented them from rubbing their eyes and thus introducing infectious material from their fingers into their eyes, but either way they made a difference.
The same Cochrane Review showed that gloves were highly effective in preventing infection. The studies on this topic took place in a hospital setting, where healthcare providers changed their gloves after seeing each patient, so wearing the same pair of gloves all day isn't likely to help. It's also very important to understand that wearing gloves does not eliminate the need for handwashing.
Protective gowns (e.g. surgical gowns) were also shown to significantly reduce infection. Again, this was in a hospital environment, but it highlights the importance of clothing as a possible fomite (an inanimate object that can transmit infection). Surgical gowns may not end up seeing much use in day-to-day interactions outside the hospital, but this finding implies that it might be worth changing your clothes after coming into contact with someone who may be infected.
All of the above, plus handwashing
Not surprisingly, the most effective intervention was a combination of all the forms of personal protective equipment above plus frequent and thorough handwashing.
4. Thoroughly disinfect surfaces where you live and work
Doorknobs, computer keyboards and mice, telephones, tables, kitchen counters and other surfaces can all transmit infection. Thoroughly cleaning these surfaces with disinfecting agents can help reduce the spread of a flu virus.
5. Use a humidifier
This study (and a few others) suggest that humidifying indoor air may reduce the risk of flu transmission. The evidence is fairly limited here, but the argument seems sound to me.
6. Practice good cough and sneeze etiquette
Don't cough or sneeze into your hands. If you don't have a tissue available, cover your cough or sneeze with the crook of your elbow instead of your hands. That way, you won't be spreading germs to everything you touch. If you do have a tissue available, you can cough or sneeze into that, then throw it away and wash your hands as soon as possible.
7. If you have children, make sure they do all of the above
Children are especially good at transmitting the flu virus, which is why schools are likely to be closed down during a pandemic. Making sure that your children learn to take the above precautions (especially frequent and thorough handwashing) can help to keep them safe... along with everyone around them.