After you have finished installing tiles on one side of the internal corner you should continue by laying tiles on the other side.
How to lay wall tiles in a corner.
As you can see in the image you should place spacers along the inside corner and between the tiles.
As you work your way up from the bottom you smear your thinset onto the wall with a notched trowel depending on the size of your.
Press the tile against the wall with the cut side facing the corner and the other edge next to the last full tile in the course.
Step 4 lay the full tiles.
Apply mortar to the back of the tile with the notched trowel.
When tiling any wall you want the cut tiles in a less visible area than the whole tiles.
Space the two tiles consistent with the rest of the tiles generally 1 8 inch which will leave a 1 4 inch space at the corner.
Treat each wall individually rather than trying to tile the room as a whole.
Repeat the entire process again vertically before screwing wooden battens into place over the lines your starting point is the corner where the battens meet.
Trim and lay edge and corner tiles when you need to trim a tile before you lay it put the tile in place on the wall mark your cutting points and use a tile cutter or angle grinder to trim the tile to size.