I LOVE the L&L skill called enforceable statements. It basically teaches you how to say something in a way that is actually enforceable. You say what you will do not what they must do.
PK Parent: Toys that are picked up by their owners are available for play the next day. Toys picked up be me disappear (or go in the toy jail until they are bailed out).
Parent of a Young Teen: I'll be happy to take you to the mall as soon as your room is clean.
Parent of Bickering Kids in the Car (pick a day when you have time and they don't): I drive the normal speed when voices are happy and quiet.
Once when I was in an argument with one of my own teens I used, "I'll be happy to have this conversation with you when you and I are both calm. Since I am not calm, I am going to Wal-mart. (I just had to remove myself from the vicinity to disengage.)
Take Care, Jill