In addition to getting one point for spotting a yellow car, there are other rules.
1) It cannot be any form of construction equipment or have any form of advertising on it.
2) Someone else has to see it and confirm it. This is to prevent someone from cheating.
2a) Yeah someone might be a dick and intentionally not look for it. If they do it a lot, just punch them in the arm and stop playing with them.
2b) Each person has two 'honor' calls. If a yellow car is called and not confirmed, a person can use an honor call. Obviously there is room for cheating here too, but only the lowest of the low actually abuse it.
3) A false spotting results in a .5 point deduction. A false spotting is when the words "Yellow Car!" are said when in fact there is no yellow car there. You can catch yourself and just say "Yello..." and not complete the sentence and still be ok. As long as the two words Yellow and Car do not escape your mouth, you are fine.
4) Everyone starts at 0 (or you can give people points as a handicap to yourself) and the game is win-by-10.
4a) This means if there is a 10 point differential between players, the person on the bottom loses.
4b) If you are a playing with a group, then the leader can knock people out and the game still can continue. It is only truly over when a person is at least 10 points ahead of everyone playing.
4c) If the point differential slips back under 10 points due to missed calls, the person who was previously knocked out can come back in to the game.
5) Calls can only be made while the car you are in is moving. This means if you are stopped at a stop light or gas station, you cannot call anything until you start moving again.
6) In the case that there are lots of yellow cars in the same area, you cannot say "YELLOW CAR!" and claim them all. You have to repeat the call for each vehicle.
Thats about it. The game rewards constant paranoid attention so it always gets real amped up if everyone is playing really hard. Other than that, there are no rules. This is where the strategy comes in. There are two main defensive tactics to Yellow Car - View Blocking and Distraction.
While view blocking is obviously more effective, you might get punched for playing like a bitch. Distraction is where its at. A good distraction is to get everyone singing a song so they forget about Yellow Car. Another good one is to give them food to eat that requires a lot of chewing so they have trouble calling out. Professional players can and will distract you without you realizing it; you have to stay on your toes.
Some offensive strategies are false half-calls (used to make the other person look at a specific place) and mirror watching.
A standard game with 4 people last about 3 hours. A bo3 on a long trip is usually the standard to determine a true winner.
Alright, now have fun!