Help with writing a book... similar to catcher in the rye?

I'm trying to write a book (similar to the cynical tone of Catcher in the Rye or Perks of Being a Wallflower...obviously my book won't be as good as these ones but I'm just bored =D). I can't seem to think of a really good starting area for the plot.. I mean I have ideas that I want to happen in the middle of the story, but how do I get a good story started.. Do I introduce the character? Do I start with a tragedy? .... Help!!!