To tile around a tub or shower start by measuring the height of the back wall from the lip of the tub to the top of the area to be tiled.
How to install ceramic wall tile around a bathtub.
If the tub is level start with a full tile at its rim.
Diycrew hrvdiy renovision step by step tutorial how to install wall tile in any shower with any size bathroom tile including how to install tile in a nic.
Then apply a generous amount of thin set to the bottom bathtub tile and position it 1 8 in.
Divide the dimension in half and make a mark there.
Above the lip of the tub.
When tiling around a tub mark the first layout line at the vertical edge of the tile next to the tub.
Apply it to the wall with the bottom edge about 1 4 in.
Follow the order shown in the diagram to snap the rest of the lines.
For a tub surround only install the backerboard and tile 12 inches above the tub.
Check if you need to adjust this mark to avoid laying slivers of tile at the top and bottom.
I cover some of the specifics of how to layout and set up a tub to install tile around it.