Electrical sockets are a tricky issue when re-tiling a wall, and not just because of the cuts you have to make around it. Sockets are set in electrical boxes that sit flush against the wall, then the plate cover is screwed on the front with the edge of the cover extending over the wall and sitting flat against it. The problem is, the thickness of your tile is going to bring out the level of your wall by about 1/4 inch, which means the electrical box will be set back now and the plate won't sit properly.
Resetting the Socket
``Box extenders'' are handy little inventions that raise the level of your socket out of the wall by about 6.35mm / 1/4 inch, so it will still sit flush with the wall after you tile. The electrical box itself doesn't move; instead, you unscrew and pull out the socket from the box (first shutting off power at the circuit box, or course). You don't disconnect the wiring, but let it hang there out of the box. Slip the backless plastic extender over the socket and into the box. The extender has screwholes that line up with those of your box. Re-attach the socket through the screwholes in the extender, then through the box. Your socket should now be sitting out from the wall.
Laying Out Tile
Don't just hope that the tiles will be in an acceptable configuration when you get to the box. You don't want a situation where you have to cut and hang a 12.7mm/ .5 inch piece of tile on one side of the box. As you're laying out your wall pattern, take the socket box into consideration. Measure to figure out where the tiles will ``land'' around the box. If the pattern is going to entail a sliver-cut of less than 25mm / 1 inch on any side of the box, then readjust your layout so that it doesn't.
Setting and Finishing the Tile
Make your measurements to take the tile right up to the side of the box extender, almost touching it. Depending on your layout, you may have to make a cornering cut in a tile around the box, which means you'll need a power tile saw rather than just a score-and-snap straight cutter. The cut sides of the tiles always go against the box. When you grout, don't fill the space between the cut sides of the tile and the box extender, but leave it open. After the tile is finished, replace the plate cover. It should now sit flush over the tile and the box.