Tiling around corners and over projecting edges, such as window reveals, is less daunting than you might think. Most of the wall will have been tiled using field tiles, which have straight, unglazed edges.
For edging fields of tiles, you can buy special RE (round edge) tiles, which have one edge rounded and glazed for a neat edge; REX tiles, which have two adjacent edges rounded and glazed; and mitred tiles, which are rounded 'strips' used for 'turning' corners. There are also plastic edging strips available in a range of colours to blend or contrast with the tiles. These are held in place while the last row of tiles is pressed into position.
When you tile around a corner or around a window, tile up to the edge, then use RE tiles on the reveal so they lap the edges of the surrounding tiles. Fitting into a corner may involve cutting a tile down to size. Keep any cut tiles for the back of the reveal.
