Okay here is the main key to it...
Firstly do //wand, and right click and left click respectively to select the same as a 3D box. Then, say you were copying a house, stand at the door of the house ground level, if you were about to enter the house, and do /compass (must have essentials installed) and the compass will show u a direction eg North. Now go to your new location, and face the direction north, keep facing directions until /compass shows north, and now, standing at ground level do //paste. Use //paste -a if you are just pasting in air or flat land, it will save you CPU and RAM usage. And thats pretty much the key idea behind it.