Installing the tiles. Once you roll up your sleeves and are ready to go to work you want to make sure that you have everything there that you are going to need.
Some discrepancy can be attractive but that's a personal design choice.
Sometimes it's a good idea to pull tiles out of different boxes as you work so any slight discrepancy is integrated into the overall look of the job. Spreading the adhesive. If you are installing tile in an area that is going to be exposed to water conditions, use a mastic that is water-proof so that it will hold up well. This is very important. If you are applying floor tile in areas not exposed to water you can use a mastic that is not water-proof.