Normally the idea of messing with an electrical outlet makes me squirm, but Apartment Therapy's quick fix for a loose wall outlet means skipping out on a costly electrician bill. Not only is a wiggly wall outlet unsightly, but it can also be a fire hazard. The solution is simple:
"Grab a $3 pack of outlet spacers online or at most hardware stores and they're a cinch to install: Just cut power to the outlet and wedge 'em around the screw holding your loose outlet to the electrical box until there's a tight fit.
These spacers also work well to bring an outlet flush with a thicker wall. If you're planning on installing bead board, stone or any other wall enhancement with thickness, you'll probably want to grab a set like these. They can 'Lego' on to each other to bring an outlet up flush with your new wall."