I have noticed the key to success is never leaving home without body armor, always use cover, and snap to targets quickly with the aim system. Snap, then move up ever so slightly for a headshot, then find the next target.

For Undressed to Kill, I started with the guy in the private room, switch to shotgun in a corner out of line of sight. Drop the guy blocking the door, then the manager inside the room as you bum rush it, then switch to the sub machine gun. Move to the entrance to the main room and take cover on either side. Pick targets carefully until everyone but strippers are dead. Last dude is outside, shoot him through the windshield of his car.