On the title screen, the one where the family are watching the TV, type "COWABUNGA" and when you start the game you'll have infinite lives. Also try typing "EAT MY SHORTS" on the title screen to enable the number keys to skip levels.
There are a few hidden extras to find throughout the level, such as exra lives and more money. There are usually hidden in bins and bushes. To find them, just jump onto them. However, you need to be careful, since some bushes contain bees which have a lethal sting!
You can get extra help by defeating end-of-level gurdians via the disgused aliens throughout the levels. To spot them, put on your X-ray specs. If a person seems to have a wibbly head with tentacles sprouting out of it, jump on top of them and they will drop a ball. Pick up the ball and get a letter, if you manage to spell out the name of a family member, that person will then appear at the end of the level to help you beat the guardian. For eg: If Maggie appears she throws rocks above your head which you can deflect towards the bady along with your nomal shots.
If you miss one or two of the targets, don't panic! If you notice the sign near the cinema, this should give you a clue. Watch out for the timer and go to the cinema when it reaches 400 and 200. At these time a person will come out of the doors. Just spray them to knock your target counter down.