Tile can be used for most surfaces in a bathroom, and is generally preferable to wood because of the high moisture content in the room. Rather than bordering tiled areas and other spaces with wood trim, which can become soft and rotten with time, consider bordering it with more tile. Bullnose tiles are finished on one edge, so they can sit directly against an open wall and form a finished border, with no additional material needed.
Measure across the span that you want bordered. Find and mark the halfway point with a pencil.
Spread tile mastic on the back of one bullnose tile, using a notched trowel. Cover the back of the tile completely, to a depth of about one-eighth inch.
Press the tile to the wall on one side of the middle mark that you made. Position it so the unfinished edge is alongside the area that's being bordered, and the finished edge is facing out toward the surrounding wall. Put spacers between the unfinished edge and the area being bordered.
Repeat the process to hang the rest of the tiles along the border, side by side, with spacers between them. The bullnose tiles should line up with their finished edges forming a new border against the wall. Cut the end tiles as needed, on a tile cutter.
Let the mastic set for eight hours. Remove the spacers.
Grout the tiles, spreading grout over them with a grout float, scraping the surface of the tiles with the long edge of the float and pressing it into the spaces between them. Let the grout sit for 20 to 30 minutes, then wipe down the tiles with a damp sponge to take up the excess grout, while leaving it in the lines. Let the grout set for 48 hours.
If the area you're bordering is a partially tiled wall, and you're hanging the border tiles immediately after hanging the standard tiles, don't grout the standard tiles until after you've hung the border tiles, then grout the whole thing at once.