If you find hairline cracks in you shower tile, the problem might not be with the tile itself. It's what’s underneath it.
Step 1 - Backer Board
The most important factor for preventing cracks in your shower tile verifying that the tile is installed over the correct materials. Use cement backer board to provide strength for the tile. Start by stripping the wall to the studs, then add a plastic moisture barrier before attaching the cement backer board. Always use this method in the shower.
Step 2 - Mortar
Use a quality thinset mortar to put the tiles in place. You can use either powdered or premixed; premixed is easier.
Step 3 - Finishing
Once the tiles are in place and grouted, seal the seams; otherwise water can cause cracks. Clean the haze from the tiles, then use quality grout sealer. Apply it properly so no water can leak behind the tiles. Allow ample time to dry before using the shower.