Large, heavy wall tiles are a challenge to hang, because the weight of tiles makes them prone to slip off the wall. In theory, the easiest solution is to build from the bottom, supporting the lowest tile course right on the floor and letting the upper courses rest on those. But in reality, floors often aren't level, which means that approach would make your whole tile grid off-level. The solution is to level and shim the bottom course, which takes some time and patience but makes the rest of the project go more smoothly.
Mark a horizontal line along the bottom of the wall, coming up from the floor by the height of your tile plus one-quarter inch. (So if the tiles are 10 inches high, the line should be 10.25 inches off the floor.) If the floor isn't level, raise the level line as needed to ensure there is no point at which it's less than the height of a tile plus one-quarter inch from the floor, even if that means some portion of the line is higher than that.
Draw a vertical line up the middle of the wall, from floor to ceiling, intersecting the horizontal line.
Spread no-sag mastic adhesive along the bottom of the wall with your notched adhesive trowel, covering everything from the floor up past the horizontal line. You will be able to see the lines through the mastic.
Set the first two tiles in place on either side of the vertical line, under the horizontal line. Put one-quarter-inch spacers between and under the tiles to separate them from the floor.
Hang the rest of the bottom row of tiles in the same manner, working your way out toward the edges, putting spacers between and below all of them. Cut the tiles at the ends as needed on your tile cutter.
Assess the spacers under the tiles, where they meet the floor. If any spacers aren't tight between the floor and the tile (because the floor is low at that point), then wedge a shim under the spacer to get it tight.
Hang the second course from the bottom, again beginning at the middle and working toward the edges. Put spacers all around each tile, so they're separated at the sides and supported underneath by the bottom row of tiles. Cut the ends as needed. Work your way up the whole wall, course by course, spreading more mastic as needed.
Let the mastic set for 24 hours. Remove the spacers. Spread grout over the wall with a grout float, press it into the joints between the tiles. Wipe up the excess grout with a damp sponge.