Cover your mouth when you cough or sneeze.
As adults, we know this, but we must remind our students. I have been known to separate students who are unable to remember to cover their mouths/noses and continually cough or sneeze on other students. This may seem extreme, but one sneezing, coughing student can quickly spread the "ickies" to the rest of your class. Another option may be to find a "doctor" mask, allow the coughing/sneezing student to decorate it, and have him or her wear it while participating in whole-class activities.
Disinfect surfaces early and often.
In an elementary environment, teachers should grab a clorox wipe or something similar and clean their desks, pencil sharpener, door knobs, and any other common items at least once a day. Enlist your students to help! As a secondary teacher, it may be a good idea to have each class wipe down their desks before they leave for the next class. Advise students to avoid touching high-traffic surfaces such as handrails if possible.
Wash with warm water and soap.
There is a lot of debate out there as to whether hand sanitizers are really good, and the same is true for antibacterial soaps. I will leave you to make your own determination about these items, but do have students wash with good, old-fashioned warm (almost hot) water and soap, and do it as often as possible.
Remind students to stay home when sick.
While good attendance is important, good health is also important. Remind students that if they come to school sick, not only will it take them longer to get better, but they can make their classmates sick also. Make sure students know that work can be made up, and establish clear guidelines for doing so. Also advise parents to have their children get vaccinated for the flu if at all possible. They make those super kid-friendly nasal spray vaccinations now, so no needles necessary!
Eat healthy, and get plenty of rest.
When we are not eating right and not getting enough rest, we are setting ourselves up to get sick. A tired, malnourished immune system is a compromised immune system! So, turn off the computer and go to bed (after you finish reading, of course), even if you haven't crossed off everything on your list. Drink plenty of water, and make smart food choices (I'm not saying don't eat cake, just throw in some fruits and veggies, and maybe swap out the ice cream on that cake for some frozen yogurt).