A backsplash is a small area at eye level, which means every imperfection is seen daily from three feet away. The tiling is easy; the layout is the job.
Set out from the focal point, not the corner
Find the visual center first. Usually the cooktop — often with a hood above it, which frames it — or the window over the sink.
Center the pattern there and work outward in both directions. A backsplash that is centered on the range and slightly uneven at the far end of the run reads as correct. One that starts full-tile in a corner and lands a sliver behind the range does not.
Never lay the first course on the countertop
Two reasons.
Countertops are not level. Even a good one varies, and a first course sitting on it inherits every variation and carries it up the wall.
The counter-to-tile joint moves. Cabinets settle, countertops expand. That joint gets silicone, not grout — so the tile has to sit above the counter with a deliberate gap, not on it.
The method: mark a level line one tile height above the lowest point of the counter, screw a temporary batten to it, and lay the first full course on the batten. Cut the bottom course to fit afterward, leaving a 1/8 inch gap at the counter for sealant.
Where it stops
Under upper cabinets: to the bottom of the cabinet, and the top course usually needs cutting.
Behind a range with no cabinet above: to the hood, or to the height of the adjacent cabinets, or to the ceiling. All three are defensible; stopping partway up a bare wall is not.
At an open end: finish with bullnose, a metal edge profile, or a mitred edge. A raw cut edge at eye level is the detail that separates a finished job from an unfinished one.
Outlets
Turn the power off. Remove the plates, loosen the receptacle screws and pull each receptacle forward so it sits proud of the finished tile surface. Box extenders are required by code where tile brings the wall face forward — they are inexpensive and inspectors look for them.
Cut tile to fit around the box with a small gap; the plate covers it. Cutting exactly to the box leaves no tolerance and one tile in three will be short.
Adhesive and grout
Dry-area walls take mastic or thinset. Mastic is easier to work with and grabs immediately, which matters on a vertical surface — but it is not for wet areas, and it does not suit glass or very large tiles.
Glass and polished stone need unsanded grout or epoxy, because sanded grout scratches both. Test on an offcut before grouting the wall.
Behind the range
That wall gets grease and heat. An epoxy grout, or at minimum a well-sealed cement grout, saves a lot of scrubbing over the years.
Count the tiles for a run and its cuts on the backsplash calculator — the outlet cuts push waste higher than a plain wall of the same area.