Which salmon. Ordinary farmed Atlantic salmon is exempt from the rule that fish eaten raw must be frozen first, and it is what I use. Wild-caught or unknown-provenance salmon is not: buy it sashimi-grade or previously frozen, or freeze it yourself at -20°C for at least 24 hours before curing.
Weigh the salt. A spoon of coarse flakes holds far less than the same spoon of fine grains, so measuring the cure by volume is how it comes out bland or inedible. Coarse sea salt or kosher salt, not iodised table salt.
The cure has to touch every face. Any bare patch stays soft and uncured. Turn the parcel every twelve hours so the brine that collects washes back over both sides.
Slicing. Twenty minutes in the freezer first, the longest sharp knife you have, held almost flat, one long stroke rather than sawing.
Keeping it. Tightly wrapped in the fridge, eat within about five days. It freezes for up to three months, and freezing the piece whole beats freezing slices.