Stephen in his book GenreScreenwriting says that people laugh because they are setup to be familiar with the situation and expect a familiar solution or answer but instead they are hit with an unexpected answer. So incorporate familiarity and the unexpected to get the laughs.
The major collision in all successful comedy is the clash of childishness vs social responsibility. Usually the protagonist impersonates someone he is not, so the more he wants to come clean it becomes more hard.
Three storytelling approaches:
1. Teenage coming of age (American Pie)
2. Body switching (ex: Big, 13 going on 30 etc)
3. Role Switching (Wedding Crashers, What Women Want etc)
