Parker,
My folks are the true masters of cedar plank cooking and they have been doing it for quite some time, long before the recent cedar plank hype. You need to make a salt rub for the fish which you just baste on prior to cooking. There are several other ways, some mentioned in posts above, but the salt rub and mom's homemade marinade/sauce over the top and it is as good as it gets.
You want cedar planks you say, Parker? Come over and get some. We have about half a tree worth of cedar rounds in the back yard which we split and plane into planks for cooking. We also have a shiatload of alder which is killer for planking salmon too! BTW, it's not just for salmon. You can cook chicken, veggies, etc. on the planks as well.