If there's a golden rule to this game, it's that some targets will trigger a new event if you hit it. The second event is worth way more points.
There's an "Easter Egg" or hidden trick to each room.
Barn Room (we shoot eggs)
EASTER EGG: The very small rat near the house at the top is worth a few points, but he's more valuable for what comes next. If you hit him when he scurries up the barn, the barn flips open with high-point mouse targets. After the barn turns back over, the rats will appear in the field with the other animals, worth 1000 points each. If you find the time, you could also shoot the goat in the top corner (2,000 pts?) and the fox on the henhouse (500). The fox, once shot, triggers a series of 1,000 point chickens.
Balloon Room (we shoot darts)
EASTER EGG: Aim for the corners. If you knock out the balloons on the cloud, you get a shower of 500-point balloons covering the screen. If your partner does the same thing on HIS cloud at the same time (more or less), then what you trigger is a shower of 2,000 point balloons, rainbow colored.
Green Army Men Plate Breaking Room (we shoot baseballs)
EASTER EGG: Hit the jumping 2000 point plates (at the same time on both sides of the screen) to activate a slew of jumping 2000 point plates across the screen. During this wave of jumping plates, you and your partner must both hit two jumping plates, and you'll unlock a tank that will come out of the mountain.
Alien Room (we shoot rings)
EASTER EGG: Put a ring around all the 100-point aliens in the rocketship in the middle. Do it before any of them pops back up, and you trigger the "hungry monster" who opens his mouth and lets you rapid fire in your rings for 500 pts, then 1,000 pts a shot. Get the monster to appear early to maximize your time with him; we find it effective to have me and my partner "split up" the spaceship to blanket it with rings very fast. Every so often, the monster keeps his mouth shut. Aim at 1,000 or 2,000 or the 5,000 point rocketships on the side during this quiet time, but come back to the monster when he's ready.
Western Room (we shoot suction-cup arrows)
EASTER EGG: In the first room here, you see many bullseyes that open up new targets when you hit them. Clear everything one time, not bothering to hit things that re-spawn, and you'll see that the targets leap up to 1,000 and 2,000 points possible.
Kill the bat at the top as soon as you see it. It flips around to reveal a 5,000 point target. Then, the mine cars start saying 1,000 or 2,000 points. When you start moving across the scene, hitting the two 500 point targets that are close to each other throughout the scene opens 2000 point targets. In the mine car part, hit every single mine car to get two 5000 point mine cars, quite tricky to hit that and the bat.
The very instant a giant target fills your screen, start rapid firing and don't stop until it's all over. As you hit the target, lights around the outside of the target illuminate. Eventually, the target starts being worth 1,000 points and then 2,000 points. But you have to be very quick.
To REALLY get the high scores for the day or for the month, what you need is a partner who is willing to work with you to open up all the bonus targets, but then let you gather all those points.