What I've been learning so far (and general comments):
1 - Shoot all the big bubbles first, then all the medium bubbles, then all the small bubbles. You get way more points that way. Watch the points appear when you shoot a bubble--if you shoot a string of same-sized bubbles, their values increase. Once I learned this, I tried to do this as much as possible. What does it get you? A field full of way too many little bubbles. Hard.
2 - Shoot all of the breakable bricks--they're worth 500 each. On some screens, where there are several, you get a free guy for shooting all of them before the round ends.
3 - I try to avoid the vulcan gun.
4 - I try to pick up every power up, even if I don't need it, because they're all worth points. Dynamite & vulcan gun are sometimes exceptions to that rule.
5 - I've been starting on round 1. I figure that's the way to go--I don't see any bonus for starting on a higher stage.
6 - Yah, the food is worth tons--when you get to southern Europe & such, it's around 50k per fruit!
7 - Collision detection really cheeses me off sometimes--there will be a bubble really close, I'll shoot, I'll die, & after my guy falls off the screen, I see that the bubble is slightly overlapping my harpoon. Baloney! I think the game checks for bubble-man collison before bubble-weapon collision...
Game on!
-Jason