sample all layers

Want the ability to do all your retouching on a blank layer??
Create a new layer in your layers pallet.
Now with that layer (blank) selected, choose either your spot healing brush, healing brush, or clone stamp.
If you try to retouch on your new layer it will not work.
Look at the options bar for the tool you have chosen and check the box beside "sample all layers" (by default it is unchecked). You can now retouch away and have all your corrections happening on the blank layer.
The benefit you ask? You can now lower the opacity of that top layer to make the retouching look more natural.