I use a wet smoker for doing all my smoking which produces a different product than dry smoking which takes a lot longer. Its not so much preservation as cooking. Since mine uses propane it keeps a constant temperature without having to screw around with it much.
Prepare the fish by brining them overnight. You can do this by adding a generous amount of salt to a one gallon freezer bag adding enough water to cover the fish and letting them set in the refrigerator overnight. In a pinch just take wet fish and rub salt all over them if your are in a hurry.
Prepare the smoker by bringing it up to about 200 degrees and adding tarragon to the water pan. Usually its best to add the wood (pre soaked in water for at least 20 minutes) you are going to use at the beginning before you put the fish on. Its a judgement call how much to add but several pinches of tarragon are usually enough. Put the fish on (spray the racks with oil so they don't stick) and bring back up to 200 degrees and walk away for 3 hours or so. Avoid the urge to check before then. If its cold and windy out perhaps 4 hours but with enough water in the pan you don't have to go to the minute as it won't burn or dry out. Make sure the water pan is full since otherwise the temp will climb and blacken the fish and possibly dry it out.
At the 3 hour mark open the door and pull them out. Remember to complain endlessly to the wife about the back breaking labor involved and how difficult it was. The skin will peel off easily and the outside will be a very rich golden color. The fish will be moist and flake easily.
Everything from there is a matter of taste and trial and error. Dry smoking is a totally different process but this is a quick way to make dinner and usually the fish will last for a week at least in the refrigerator. I use oak or applewood but as long as you stay away from hickory or pine in particular its what tastes best to you.
I'm sure someone will have a better way to do it but life is complicated enough without adding additional layers. I've mostly used this with trout and salmon but pretty much works the same for any kind of fish.