Here's a few tips I got from a well know company's website concerning your issue. I do hope this helps a little 
Stay Hydrated
It turns out that drinking plenty of water will not only counter the overall dehydrating effects of air travel, which can lead to headaches, stomach problems, cramps, fatigue and more, but can actually fortify your preemptive natural immune mechanisms to function considerably better. As your body dries out, your nose and throat go with them. Of course, this is the case in normal daily life -- when exercising, during prolonged sun exposure, etc.; even caffeine and alcohol consumption can dry you out. However, in an airplane, where your nose and throat are on the front lines of the war with exceedingly dry air, these are the first places to suffer; most travelers have felt the sting of a brutally arid mouth, throat and nose in flight. Sipping water or some other fluid regularly throughout the flight may be more effective than drinking a lot of water at one time before or during the flight; this will keep your protective system from long dry spells. (And we do mean to single out water here -- as noted above, alcohol and caffeinated drinks such as coffee or sodas can actually dehydrate you.)
Nasal mists have been found to be very effective in keeping this system working in your nose. Additionally, hot drinks are a good way to keep your protective mucous membranes working -- first, to assist in keeping you generally hydrated; second, by triggering the system into gear; and third, by directly providing moisture in the form of steam. Note that this is not a treatment per se; rather, it just keeps your defenses strong and functioning.
Keep Your Hands Clean
Your hands are the most consistent point of first contact with cold, flu and other germs. It is a direct line from armrest/seatback/handshake to fingers to fork to mouth to full-blown fever a few days later. According to a
National Institutes of Health factsheet, the type of virus that causes the common cold and the flu has been found to survive for up to three hours on your skin or on objects such as armrests, TV remote control handsets, tray tables and other similar surfaces. However, the simple act of washing your hands with hot water and soap is a formidable rampart against this transfer of harmful microorganisms.
Hand washing is not just for restaurant workers and travelers; health professionals and researchers working to combat communicable diseases in many third-world countries are waging a fierce campaign to encourage residents to adopt this simple practice into their daily routines. If possible, wash your hands before any
in-flight meals, and after your flight as well.
Of course, airplane cabins are tight places, and getting out of your seat to wash up before and after every snack time can be almost impossible, as the flight attendants command the aisles, your seatmates are trying to eat, tray tables are down cabin-wide, and no one involved really wants to have folks getting up and down and roaming around the cabin. (Even on the ground, the water in many locations can carry water-borne bacteria that may not agree with all Western constitutions.) In these cases, the Centers for Disease Control and Prevention recommends alcohol-based products made specifically for washing hands.
Take Your Vitamins
The rapid response effect of vitamins is unproven, but many travelers swear by them. Charles Westover, a retired VP of fleet management for a major shipping company, starts taking vitamins two days before flying. "I have no idea if it helps at all, but of the hundreds or thousands of flights I have taken, I rarely get colds," he said. "I just take a standard multivitamin, and it has never let me down." The NIH concurs, sort of, offering that no conclusive data has shown that large doses of vitamin C will prevent colds, although it may reduce the severity or duration of symptoms.