Hi jimcam,
I don't know if its the right way but what I did was cut the upright tile trim level with the top of the tiles then mitre the horizontal trim a bit of careful trimming with a stanley knife to remove the points then grouted, doesn't look too bad.
I'm sure one of the tiling experts will be along soon to give you the right advice.
There a bit like buses you wait ages for one then three will come all at once