In most cases tiling a window sill and grouting the tiles takes a few.
Tile trim around window sill.
Set tiles spread and comb thinset.
Then measure around the window as to cut the tiles with a score and snap cutter or a wet saw to fit into location.
Select tiles in a style that accents the decor of a room and include bull nose tiles to trim the outer edge of the sill.
Use bullnose tiles to round off the edges of the window frame and tile the wall first.
If the trim tiles are the same length as the edge tiles count the number of tiles along the edge then buy that many trim tiles.
If your trim tiles are larger or smaller than the tiles along your edge measure the edge of your tiled surface then divide that number by the width of your desired trim tile.
Paintable silicone caulk can be used around the outside of window units to properly seal the window and the siding edge or around the entire door unit.
That way you can make sure the grout lines of the recess are on the same plane as the wall.
Pry off the trim and build a molding from milled stock.
Since this video i learned about a router bit for profiling the edge of window sills which is easier.
In order to tile around a window you have to spread thin set on the wall by using a notched trowel.
How to tile around a window with wickes subscribe to the wickes here.
When installing the tiles around windows make sure you first secure the tile corner trim in thinset.
Use around the perimeter of windows to help seal the window to the header sill jack stud and jamb.
The edge you will be.
Use around sinks tubs and showers.