Alien: Finish your drink whenever someone talks with mother, and take a shot every time Lambert panics.
Aliens: Take a shot whenever Ripley rolls her eyes, sighs, or looks generally pissed off.
Alien 3: Take a shot whenever someone mentions the rescue ship or says the words 'dragon', and finish your drink when they claim they have no weapons or icecream.
AR: Take a shot every time they do a close up of somebodies eye with a strange circle of light in it. (The scene at the chapel will be your biggest challenge.)
Predator: Drink through the cleaning of the skull, and take a shot everytime there is a closeup of a beefed up muscly arm.
Predator 2: Take a shot whenever the city is made out to be an exaggerated warzone, finish your drink when you see from the Predator's point of view.
AvP: Take a shot whenever someone says 'sacrificial chamber', 'serpent' and 'hunter', and finish your drink when the pyramid shifts.
AvPR: Drink for the first 10 minutes straight, pass out, and be thankful you didnt have to watch the whole thing.