Following this rules:
Rule one: Don't be a hero.
Rule two: Get a weapon, even a knife will do, being completely unprepared is stupid.
Rule three: DO NOT search for aliens, avoid all unnecessary contact, just fight to defend yourself.
Rule Four: Your life is way more important than anything else, except maybe a twinky.
Rule Five: Try to "make a party" with guys that look bad ass, and possibly girls, you need food after all.
Rule Six: When entering a room where you plan to stay over 30 seconds ALWAYS check closets, bathrooms, under the bed (optional) and behind the curtains, after all aliens love hiding under your bed.
Rule Seven: Attempt to get to a place similar or equal to an atomic bunker, where you can live around 20 years without the necessity of going out.
Rule Eight: Have you considered suicide?
Rule Nine: Wear a 1ton armor and go Master Chief on all the aliens, which happens to go against rules one, three, four and possibly five.
Rule Ten: Have sex at every chance you get, including inter-racial intercourse. Who knows, maybe alien girls will like you and have you as a pet.
Rule Eleven: Kill everyone who attempts to blackmail you in ANY way.
Rule Twelve: Avoid family, it would be awkward if you had to abandon them to save yourself, probably.
Following those rules you will survive the longest time possible, unless you are the President of the United States, in that case call the Men in Black.