What is the tile tip in this photo? The tip here is to be creative. I used a scrap drywall bead to help hold the top tile in position. The bottom tile is all ready set.[/QUOTE]
Look close in this picture from an old tip of mine. See the mitred corners. See the gap between the tiles. I often make the bevel not 45 degrees but rather 50-60 degrees. This allows the grout a little more room and makes for a slight dovetail shape.
The second tip is that the tile spacing needs to be perfect. Look at how the grout line continues from right to left. The top tile in the niches face level with the top edge of the tile on it's right.
If you keep that going on it looks great in the end.
This photo is close to what I do. I think the back befell needs to be more than 45 degree's personally....