Lay the tiles out on the floor or hold them in place around your center tiles to make sure the pattern looks correct. If the tiles won't fit evenly around the edge, use a score-and-snap tile cutter to cut the corner tiles to size.
Apply adhesive such as thinset or mastic to the border area of your project. Spread the adhesive with a notched trowel, keeping the adhesive to a small work area so you can apply the tiles before the adhesive sets. Plan to work with no more than eight tiles at one time.
Press each tile firmly into the adhesive, beginning at one corner and working around the edge of the project. Leave the same amount of space between the subway tiles as you left between the central tiles of your project. Use spacers between tiles if necessary. When all of the tiles are laid, allow the adhesive to dry overnight.
Spread tile grout over the dried, set tiles with a rubber grout float. Move diagonally across the grout lines, packing the grout into the spaces between the tiles. Clean the excess grout from the surface of the tiles with a soft, damp sponge. Allow the grout to set completely.