What's more important is your ability to dodge enemy bullets and things like trees and columns. If you ram an object you'll lose a chance. Some of these objects can be destroyed, but many of them cannot. So focus less on what you are destroying and work harder on just getting through the stages alive. At the end of every stage you'll find a boss.
Bosses have one or two weak points on their bodies.
Most of the time you'll have to hit a boss in the head. Each time you hit a boss in the right spot, it will change color. There are some exceptions to this rule. For instance, the second boss simply needs to be hit once in the center and it's destroyed. Sounds easy, but it's really not.