The cedar plank is usually soaked for a couple of hours then oiled and preheated.
Here is a recipe I found for this dish.
2 salmon fillets
2 thin untreated cedar planks
lots and lots of ginger, chopped
2 tablespoons lime or lemon zest, chopped fine
2 tablespoons orange zest, chopped fine
salt and pepper
Cajun or Creole spice mix
This is a variant of a signature dish of Emeril Lagasse (of the TVFN fame).
The original recipe used horseradish and trout instead of ginger and salmon.
Preheat your grill and oil up one side of the cedar with your olive oil. Sprinkle a bit of the Cajun seasoning on the plank, and lay the filet of salmon on top. Season the filet with salt, pepper, and the spice mix. Cover the filet completely with the ginger and zest -- this adds flavor and helps the fish retain all of its moisture. Put the whole thing directly on the grill over the coals, close the lid, and stand back! The thing will smoke like crazy for a while. Check on the salmon after 15 minutes. If the plank catches on fire before the salmon is done, simply spray it with some water.
When the salmon is done, you can either serve the whole thing with the cedar flaming around the edges, or remove it from the cedar plank and serve.
You may wish to remove most of the crushed ginger topping as it is a bit overpowering.
You can use seasonings of you liking, but at least this is a general guideline to use.