Make sure the top of the shower enclosure is level. Place a tile against the wall on top of the enclosure, mark the wall at the top of the tile, and draw a level reference line around the entire area to be tiled. If the enclosure is not level, base your reference line on a tile placed at the lowest point of the top of the enclosure.
Locate and mark the center point of each area to be tiled.
Make a dry run, lining up the edge of one tile with the center mark and leap-frogging tile pieces side by side to determine how many pieces will be needed and what the corner pieces will look like. If the corner pieces would be very small, repeat the dry run, centering the first tile on the center mark. This will allow you to cut larger and more attractive corner pieces.
If the top of your enclosure is not level, you will need to use the reference line as a starting point to help you keep the tiles level. You may want to line up the top of a board with the reference line and attach it to the wall for added support when you apply the tiles. After the tiles are in place, remove the board, cut tiles to size and install them in the same manner as corner tiles.
Spread a large dollop of mastic adhesive on the wall with the notched trowel. Spread the mastic up to the reference line (Image 1). Then spread it horizontally (Image 2). Hold the trowel at a 45-degree angle when spreading mastic. The notches on the trowel help ensure an even distribution.
Beginning at the center mark, set the tiles firmly in place in a straight row, making sure the spacing lugs are pressed tightly together. Do not set the corner pieces in place yet unless no cutting is required.
After the first row is complete, begin on the second row (Image 1). Repeat this process until the tiles are at the desired height. Periodically check your work to make sure the rows are level (Image 2).
Cut the corner tiles to size, using a tile cutter (Image 3) for straight cuts or a tile saw for irregular cuts (Image 4).
Set the corner pieces in place with the cut edges facing the corners. This will make them harder to detect when the project is finished.
Place mastic directly on the backs of the bull-nose tiles (Image 5). This process, known as back buttering, allows you to put the appropriate amount of mastic on the tile without worrying about putting too much on the wall.
Allow the mastic to dry, then mix a batch of grout according to the manufacturer's instructions. Grout is typically mixed to the consistency of peanut butter.
Spread a liberal amount of grout onto the tile and work it into the joints with a grout float (Image 1). Hold the float at a 45-degree angle, and spread the grout in several different directions to make sure it gets into all the joints.
When the grout sets up and forms a powdery film, wipe away the excess from the tile surfaces and the joints with a damp sponge.
Caulk the areas where the tile meets the shower enclosure as well the corners and along the edges of the tile work (Image 2).
Allow the grout to cure according to the manufacturer's recommendations. You may need to dampen the grout periodically. You should be able to use the shower after about 24 hours.