Prepare the walls of the shower. Hang the cement backer board using roofing nails or galvanized screws and seal the seams with mesh tape and thinset. Allow the walls to dry overnight. If you're installing the glass tiles on the floor of the shower, allow the mortar bed shower pan to dry at least seven days before you start.
Create a storyboard slightly shorter than the height and length of the shower stall. You do this by laying out tiles and grout lines on a board evenly spaced from the center outward. Hold the horizontal board up and mark the centerline, extending it all the way across with the use of a level. Then, at that line hold the vertical story board up and mark its center and draw the line all the way up and down. Where the two meet, you'll lay the first tile.
Cut the tiles for the corners if necessary. Once you lay out the tiles, you'll know how large to cut the corner tiles. Pieces against the back wall corners should be equal on both sides. Use a special saw created especially for glass tile to do the cuts. The saw even cuts circles so you can work around the showerheads.
Spread the thinset. Glass tiles, particularly those that aren't opaque, require a little different technique than ceramic tiles. It's a three-step process. First, spread the thinset with the flat edge of the trowel. Next, distribute it evenly with the notched edge of the trowel. Last, flatten any ridges with the flat side of the trowel. Ridges show through the glass. Be particularly careful to clean the tiles thoroughly before you apply them, as dirt also shows.
Clean clear tiles with a dry cloth and butter the back with thinset before you apply them. You also need to have a uniform coating of thinset on all the tiles if they're clear. Any mistakes here show. Outside of special tools to cut the glass and application of the thinset, the job is just like laying tile.
Measure out any area that needs cutting for the fixtures. Use the special saw for glass tile to do this. If you're adding a border, you'll need to make miter cuts in the corner at a 45-degree angle to make them fit. Bar liners for borders also need to be back buttered. Allow the tile to dry overnight.
Apply the grout. When you clean the grout, the less water the better. First use a dry cloth to wipe away excess moisture. Use a damp sponge to remove the grout from the tiles, and then dry again. Wait 1/4 hour to allow a haze to develop. Rub off the haze with a clean cloth until the tiles shine. Allow the grout to dry for a day and then use the traditional grout cleaner. Wait for several days before you seal the tiles. The glass doesn't absorb any moisture from the grout so it takes longer to cure.