You can reassign your upgrade points at any time; use this to your advantage. If you are damaged and need to hide and heal underwater, decrease your Size (so you can avoid attacks) and increase your Regen and possibly your Breath, Diving, and Bonus as well. Increase Size, Speed, and Toughness for attacking ships. If you need to attack aliens or get the bird or moon achievements, increase Diving and Boost. Leave one weak ship alive at the end of a level (and increase your Hunger) to give you time to focus on the achievements. Try to get as many achievements as you can early on otherwise the game may get too difficult and you could get stuck on a level.
 "Moby Dick 2"){kind=icon}
 "Penguin Overlords"){kind=icon}
 "Freeway Fury"){kind=icon}
 "Toss the Turtle"){kind=icon}
 "Elephant Quest"){kind=icon}
 "Bubbles 2"){kind=icon}
 "Stunt Crazy"){kind=icon}
 "Endless Zombie Rampage 2"){kind=icon}