a simple answer leads to a dead thread..
For nose butters: i start forward into a rail and lean my weight forward and on the inside edge of the way i spin(ie. spin left, weight goes left)  and then pop off the nose of your skis, basically a hop. and land on rail/box/whatever.
For tail butters: i start switch and do basically the same thing as the nose butter but i put the weight in the backseat as i come around from switch to foward and then pop off my heels and land on rail/box.
now granted this can vary for other people.  try out some different ways and whatever feels comfortable... and if you have a stiff ski.. shin bang will occur.. softer skis work well.. i have the TMs and they butter nicely.