Here are my top tricks so far:
1. Barn Room (we shoot eggs): I 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. The rat near the house at the top is worth a lot of points, but he doesn't come around very often.
2. Balloon Room (we shoot darts): Aim for the corners. If you knock out the balloons on the cloud, you get a shower of 500-point balloons covering the screen. This is key: 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.
3. Green Army Men Plate Breaking Room (we shoot baseballs): There has got to be a trigger here somewhere for secondary targets that offer higher points. But I can't find it! So I'm stuck so far just shooting the 500 and 1000 point plates.
4. Alien Room (we shoot rings): This is key: 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.
5. Western Room (we shoot suction-cup arrows): All the targets here splay open additional 500 and 1,000-point targets. Just keep shooting fast. Is there a hidden trick here?
6. Transition to next screen: keep shooting as your vehicle moves to the next screen. Some 2,000 point targets appear near the middle.7. Mine Cart Finale (we still shoot suction cup arrows): 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. This is key: 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 in order. After you make it all the way around, the target starts being worth 1,000 points and your lights start over. I can make it almost to halfway around the 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.