I've looked through a dozen books on tiling, but I haven't seen this mentioned anywhere. I know how to tile, but I haven't seen this specific problem yet. Let's say A) you want to tile only part of the wall, such as in a kitchen backsplash, or a bathroom tub surround. B) the wall is already painted and you're not repainting.
So how do you get a good line at the edge of the tile? In other words, how do you make sure the adhesive doesn't go past the edge of the tiling area, and the grout doesn't either? Could be as simple as blue taping at the edge of the tiling area, and then taking the tape off before the adhesive dries, then repeating for the grout. But I just haven't seen it ever mentioned.