how much sound deadener?

heres another question for y'all get some sound deadener just wondering should i put on the out skin in the doors or just behind the door panel??? what would be the gain of either one or both?? which should i do first(if both is really needed)???? should i do the floor of my trunk or get the sides of the car first?? im doing the trunk lid maybe 2 layers of 50 mil deadener what would i need to do next???roger (95 cougar 4.6 stock expect the stereo)

i guess i will just cover the outside skin and move to the side panels then the trunk right?roger (95 cougar 4.6 stock expect the stereo)