How do you season/prepare a wood plank for Plank Grilling?

I don't season the wood at all. I buy the planks from the local grocery store or hardware store and soak in water for 8 hours. The planks often say 1 hour is enough, but I think this is just marketing, it never seems to be enough. Weighting the plank down to keep it fully submerged will help the process.

When you're ready to cook, put the plank on a hot grill and leave it for 3-5 minutes. Once the plank starts smoking, then it's ready for your food. Don't leave it too long or it will catch fire and not smoke well as the bottom gets charred.

You need to cook this with the lid down in order to keep the smoke contained around the food and also to keep the plank smoking rather than just catching fire. You might need to play with your airflow on a charcoal grill to get maximum smoke.

Depending on what you cook, you can sometimes use the plank a second time. Although this doesn't work with Salmon, as the skin often gets left on the plate.

The main thing you need to do to prepare a plank for grilling is to soak it in water first. Otherwise, it can catch on fire and you'll have a mess.

For seasonings, you can use anything that you would use when roasting something. For salmon, you could put down some lemon slices and rosemary.

Wanted to comment on yossarian's answer, but ran out of characters.

I have some planks that I always soak overnight, which work great and rarely catch on fire. Went to a friend's house this past weekend and soaked them for 2 hours, which is past the 1 hour "recommended" time. They flared up bad within 5 minutes, to the point where we couldn't even really salvage the plank with a sprayer. I highly recommend 8 hours minimum, preferably overnight as well.

Speaking of sprayer, you'll want to keep a small spray bottle of water nearby to deal with any flare-ups around the edges - with the lid closed, the flame will climb higher than when it's open, and the planks are likely to catch at least once or twice if you're not careful (or even if you are!). Keep an eye on it, nothing like going inside for 5 minutes and coming back to a charred mess.

I recommend making sure your plank is large enough that you have 1" of clearance around all sides of the fish, in case there is a flare-up, the edges of your fish don't burn. I've experimented with keeping one side of the grill turned on, and keeping the plank on the side that's turned off, but I've gotten much better results keeping the plank side lit, on low, and just keeping a close eye on it.

Once done soaking, I lightly pat dry (with a paper towel) the side that the fish will be on, then brush it with oil so the fish doesn't stick.

You definitely want to weigh them down as yossarian suggested. Some people recommend an aluminum can from your pantry, however, I've found that this leaves rust rings sometimes, especially when soaking overnight. What I usually do is take a large casserole dish, fill with water, put plank in, put a smaller casserole dish on top, and fill that one with as much water as necessary to hold the plank down.

The rule of thumb I've always read is to soak them for 1/2 hour per inch of length so if you are using a typical 12" plank 6 hours should suffice.

As far as preparing the plank I like to finish the soak in red wine and then add salt, pepper, roesmary and some lemon slices.

Great link I've referenced in the past for this type of stuff: http://backyardprovisions.com/blogs/our-grill/11362737-soaking-your-planks-with-creativity

Good luck!