Step 1 : Plan the project
Ceramic tile can be installed directly over wallboard, plaster or existing tile. But tile must be attached to a sound surface that is structurally strong enough to support the weight.
At least one vertical and one horizontal line should be marked and extended across the wall using a 4-foot carpenter's level. The horizontal line should be level and indicate the top of the first row of tiles. If you are using a standard 4 1/4-inch square tile, this layout line should be located 4 3/8-inches above the tub. Make the layout line level even though the tub may not be. Make another plumb vertical layout line somewhere near the center of the wall.
Cut a straight 1x2 batten a few inches shorter than the width of the back wall. Nail the 1x2 in place so that its top edge is level with the horizontal layout above the rim of the tub. This 1x2 batten will temporarily supports the second row of tiles.
To help visualize the layout, place a row of tiles on the batten. Make adjustment by sliding them back and forth until the end tiles (that must be cut) are about equal. Mark their location on the wall a marker.