Always make sure you are using the proper weapon for your current situation. New weapons are rewarded for defeating Bosses. Besides their range, specific weapons may be effected by the environment. For example, the pea shooter's range is very short when fired underwater, the flame gun is ineffective, the bubble gun's rounds float to the surface, but the wave weapon remains unaffected. Use the bubble gun to deal with traps and enemies that are positioned below you. Upgrade the pea shooter to the laser and use it to take out a Boss's armor.