Condensed from a CoasterFEV post earlier this year (helped me immensely!):
Here are a few helpful hints on getting a high score at MIB:
1) NEVER let up on the trigger. The auto-fire will work faster than you can.
2) Going through scene 1 (the "shooting gallery" area) your goal should be no less than 25,000.
3) Remember, your gun uses an infared beam that gets bigger the farther away it is from the source. In other words, keep your sights and your aim on every target that is farther away from you - you have ALOT better chance of hitting it. Don't waste your time on the targets close up.
4) All aliens that are in the windows that open and close are worth more points (since you can't hit them when the windows are closed).
5) Even when there are no target aliens in sight, NEVER let up on the trigger. There is a "small child with absolutely no aim" program built in. This means that for every certain number of "misses," the computer will register a few thousand points. (they add up quick!)
6) If you are going for a high score as a group - if EVERYONE in the vehicle hits the "red button" at the same time (obviously needs some communication between riders) - then EVERYONE will receive the bonus.
7) Once the vehicles are scanned and you are instructed to shoot the "fusion exhaust port" on the other vehicle - FORGET THAT! Shoot the Fusion Exhaust Port on YOUR OWN VEHICLE!!!! Each hit is worth ALOT of points and the scoring doesn't differentiate whether you are shooting your own, or your opponents vehicle. (warning - will cause ALOT of spinning for you!)