Tiling a shower wall starts with what's behind the tiles. While on any other wall, you can tile directly over the drywall or plaster, that can cause problems in shower walls, because moisture can seep behind the tiles, softening the walls and causing the tiles to crack or fall. Shower walls should always be covered in cement board, which is a flat, moisture-proof wall material. If you're building a brand-new shower stall, the cement board can be affixed directly to the studs in place of drywall. Otherwise, lay it over the existing wall material.
Locate the studs in the shower wall with an electronic stud finder. Use your pencil and level to mark vertical lines over the whole area, showing the stud positions.
Measure the height and width of one wall. Cut out two of your sheets of cement board to equal that dimension when stacked one above the other. Use your jigsaw to make the cuts.
Measure from one side of the wall to the stud lines that you drew, noting how far each line is from the end. Transfer those marks to your sheets of cement board, marking out the stud positions on them with lines.
Measure and mark out the positions of the shower head, faucets and any other fixtures or obstructions. Cut out the holes for the fixtures in the cement boards.
Spread thinset mortar over the whole wall with your notched mortar trowel. Press the boards into place on the wall, first the lower one, then the one above, with a horizontal seam between them. Shoot galvanised drywall screws all along the marked-out stud lines on the boards, every 6 inches, to secure them. Repeat the process for each wall.
Press mesh drywall tape along every seam between the boards, and in the vertical corners. Cover the tape with thinset mortar, getting it smooth and flat. Let the mortar set for a full day before tiling.