A must read.
Here is just a taste of his Rules for the Writing of Plays
5. Choose whether or not you will write a Drama or a Comedy before you decide if anyone in the play has cancer.
6. That joke you heard over coffee that seemed so darn great when your friend explained it in detail, his eyebrows going up and down while he did all the funny voices? Do not use that joke. It is not as good as you think.
There's more. Enjoy