I just completed my first backsplash, and overall I'm pretty happy with the result considering it's my first one 😃
One question I have is how could I've avoid that first uneven tile, which is a bit proud on on the left side because of the tile edging thickness (see pictures below). I used a v-notch trowel with mastic. The tile edge is just a 6mm plastic trim. The v-notch trowel didn't leave enough glue to bury the edging thickness as far as I know. Maybe I should have "build-up" that first subway tile a bit?