Hold the tile in place against the electrical outlet. Line it up with the outlet exactly where it will be placed in the tile mastic during installation.
Make a short horizontal mark on the tile with a wax pencil where the top or bottom of the tile notch should be. Make a short vertical mark on the tile where the side of the notch should be.
Draw longer lines to join the two short lines, which will form an outline of the tile notch. The notch should be exactly at a 90-degree angle. Hold an angle square against the tile to check the angle of the notch. Adjust your marks if necessary to achieve a 90-degree-angle notch.
Score the two lines of the tile notch with a carbide tip pencil, guided by a straightedge. Place the tile nippers on the bottom line, and gently nip the tile. Place the tile nippers on the vertical line of the notch and nip the tile.
Discard the piece of tile that has been notched out. Sand the tile cuts with a grit rubbing stone until the cuts are smooth. Hold the tile in place against the electrical outlet to check its fit.