The purpose of a splashback is to protect the section of wall behind a sink from getting wet, as moisture would ruin the plaster. The easiest way to make a tile splashback is to only use full tiles, which will ensure there will be no cutting needed.
To begin, measure your sink and put a mark on the wall precisely in the middle. Put a full tile on each side of the mark; use spacers between each tile, and work outwards. Keep going until you reach the sink’s edge, or are just past it. Repeat the same procedure for a second and /or third row of full tiles (depending on how high you want your splashback to be).
It is a good idea to set the tiles out before actually fixing them to the wall to see if they end where you want them to. If the tiles fail to reach both ends of the sink, or extend further past the edge of the sink than desired, simply move the middle tiles; instead of starting on either side of the centre line you drew, place the first tile on the line, and then work outward. When you are satisfied, apply adhesive to the wall, and fix the tiles.
When tiling a splashback it is important make sure the tiled area sufficiently covers the portion of wall that will be exposed to splashing. It is also important to ensure your rows of tiles line up perfectly and have a neat and accurate border on both side edges.