For wall installation, first draw your horizontal and then a couple of vertical lines that you'll need to line up the start of your tiles. If you are doing a large space, check to see that you have a 90 degree angle at each vertical line and then check the distance between at least 2 vertical lines at a high point and low point on the vertical lines. These 2 measurements should match. If they don't match, then you know that your wall leans in or backward to the room. This is helpful to know so you can compensate for this when placing the tiles. If the wall is leaning backward, the wall width towards the top of the wall will be greater than at the base of the wall. Conversely if your wall leans in, the wall width at the top will be less than at the base of the wall. Laying your tiles in an offset brick pattern will hide these discrepancies. Laying your tiles in a straight grid pattern (like a checkerboard) will highlight these discrepancies.
Your drywall should not be primed. If the wall is already primed or painted, use a fine sandpaper to rough up the surface area. Wipe off the dust that you've generated by sanding before proceeding with the adhesive. You will be applying 2 coats of adhesive for wall installations.
Next simply roll our adhesive on the wall or you can use a paint brush to apply the adhesive if its a small area. Wait until the adhesive dries to tacky and clear state (about 30- 45 mins.), then apply a second coat. Wait til the second coat of adhesive is clear before starting and you'll be able to see your lines again. Align one corner of the tile against your 2 lines and then carefully push down the rest of that tile. Carefully align the edge of the next tile to the first one and continue to stick the tiles to the wall. Carefully place each tile tightly against the next one because once the tile sticks, its very difficult to remove. When the tile is in place, smack the tile with the palm of your hand all across the tile to ensure that all parts of the tile have made contact with the wall adhesive. You then must use a rubber mallet or a hammer with a batten board to make sure all parts of the tile are secured to the wall. Using a hand roller is not sufficient.