Regardless of what you are using for coping , be it brick, stone , cantilever or something else , the tile always goes on first. While it is possible to do some minor adjusting to the height of the tile, it's mostly predetermined by the skimmers and the pool beam. Whoever formed the pool and set the skimmers should have already taken into account the grade for the deck and coping. Several things should be checked. The highest place on the beam should be slightly lower than the skimmer/s. I try to keep the skimmer throat as level as possible. The top of the tile should be level or slightly higher than the highest place on the beam. Nail boards in place to set the tile on. Use a water level to set the boards. I use 3/4 inch Styrofoam cut in 4" strips for tile boards but a lot of tile setters use expansion joints. Doesn't really matter as long as it's wide enough to set the tile on top of and flexible enough to bend around the curves of the pool. Don't try to just stick tile on the pool wall and hope that it's level. If it's a straight wall pool , pull strings on each wall and lay the tile to the string. Make sure tiles are level vertically as well. On a free form pool , you can pretty much just go with the flow unless a radius is obviously out of whack. On a straight wall, you may have to do some browning out before setting the tile. the strings will let you know this.Some people use mortar for browning the beam out ,I always use sand and portland cement. guess it doesn't matter , just how I was taught.Once the tile is set and tight, you can brown out the top of the beam with sand and cement as well if you want everything to look pretty. Never really seemed where it mattered as something is going on top of it anyhow.