Spread a drop cloth over the shower pan and mask off the edge of the shower pan with painter's tape.
Use a drill with a paddle bit to mix thins et tile adhesive according to the manufacturer's instructions. The adhesive should be about the consistency of cake frosting.
Use a 1/4" x 1/4" notched trowel to spread thin set over the first area to be tiled. Hold the trowel at a 45-degree angle to spread the adhesive, then use the notched edge to leave grooves in the adhesive. These air pockets help the tile adhere better.
Note: Be careful not to spread too much thinset at one time; if it dries out, the tiles won't stick. To test the thinset, press it gently with a finger. If it isn't sticky enough to come off on your finger, it's not sticky enough to hold a tile.
Measure and mark the center of the first tile. Line this tile up with the reference lines on the cement board so that it's flush with the horizontal line and centered on the vertical line. Press the tile into place, giving it a wiggle to help it seat properly in the adhesive.
Continue setting tiles, working out from the center. Use tile spacers to create even grout joints. Sponge any excess thinset from the tiles during the installation.
Allow the adhesive to cure according to the manufacturer's instructions. Mix and apply grout once the adhesive is cured, then apply grout sealer after the grout is cured.