I have started to preheat the planks on the grill for 3 minutes, then turn over and put the chunk of fish on the plank. Mrs. K prefers Alder. I prefer fence pickets. I think the first time I had planked fish was at some fish joint in Seattle. They seem to have a lot of fish there. I do not try to reuse the planks. And my gas grill works just fine - although it would be fun to try this on my big green egg.
Happy grilling and smoking all!