During the game, you'll see an oval object that has three little circles above it. Look at the colored circles above the object. If the your weapon's color matches the color of the circles, you can shoot the object and get a 1-Up or 2-Up.
Increased Bomb Strength
When you use a Destroyer Bomb, pause the game. Leave it paused for about 20 seconds, or else pause and unpause quickly. This will make the bomb do much more damage.
Level Select
At the title screen, press Up twice, Down four times, Right eight times and Left 16 times. You will hear a destroyer bomb go off. Press Start and you can choose any level.