Buy a cedar plank. Soak it in salted water for a couple of hours
Rub the salmon with olive oil and season it with a little bit of salt, I use kosher salt or smoked sea salt but regular table salt will work just fine. Then put the salmon on top of the plank, skin side down. Then put the plank on the BBQ. You can see the fish cook, it will get pinkish-white starting from the skin and traveling up. If your grill has a top, close it and cook for about 20-30 minutes. Check it to make sure it's not drying out. Internal temp should be around 130 or so.
I am projecting here, perhaps, but I think the question you're asking is "why doesn't my salmon come out moist and succulent like what I get at the store?"
A couple reasons.
First: you want to properly cure the salmon for at least 24 hours beforehand. 36 is better. To cure, you will need two whole sides of salmon (or one cut in half), with the skin on. Rub your cure into the flesh--so 2:1 salt:sugar, plus whatever other spices you care to use. The addition of brandy sounds lovely; I like tequila or a nice peaty/smoky Scotch myself, or maple syrup (but obviously nix the sugar if you're doing that). Place the two pieces together, flesh to flesh, optionally including herbs between. Wrap very tightly in plastic, completely sealed, bung into your fridge to let it cure.
Second: when the fish is cured, remove from the wrap, rinse off the cure.
Third: time to smoke. If you want dry and flaky, hot smoke--this seems to be what you're doing and what you don't like. Therefore, it's cold smoke time. The two basic ways to do this are either to add LOTS of trays of ice to the smoker itself, or to route the smoke through a cooler filled with ice and then back into your smoking chamber. A quick Google should provide you with diagrams for doing so.
Do not over-smoke. Fish picks up flavours quite readily, and will dry out if oversmoked, even if cold. Really for salmon I don't think you need much more than 20 minutes of cold smoke.
Best Answer
It's pretty easy:
I'll often do this while smoking a Boston Butt, which is an all day affair. If I've got room, I throw a salmon fillet on in the middle of the day for lunch.
If you're just getting in to smoking with the BGE, I highly recommend the book Smoke and Spice.