Blackening is pretty easy. My favorite spice is called Paul Prudhomes blackened redfish magic.

publix. cast iron pan is a must

The key to blackening is to not oil the pan in my experience. You dredge fresh fish in butter, and apply the spices.(don't skimp on the spices) The iron skillet keeps even heat (and you want LOTS of heat). If it's smokin' you're doin it right brother.

Here is an excerpt from another site:

"Blackening is the process of cooking fish by coating in spice and cooking at extremely high heat. The process actually creates a barrier between the food and the heat, allowing blackening, not burning, to occur.
To blacken properly, a cast iron skillet or grill plate is heated over very high temperature until just short of a white spot or ash appearing. (The skillet or grill must be extremely dry before it is heated.) The fish to be grilled should be at room temperature. Dip fish into melted, clarified butter, then sprinkle with spice (notes: for more flavor, roll fish into spice mix before cooking and the butter can be omitted to reduce calories). Place the fish onto the pan, cooking for 1-2 minutes on each side. Blackening adds a distinctive flavor to fish while creating a savoury, moisture-retaining barrier around the outside. The result? Warm, smoky grilled flavors and succulent textures. The high heat required by blackening means that you will need a skillet or pan made of cast iron. There is really no substitute. Also, blackening will create smoke… (and how!). Work in a well-ventilated area - outdoors using a gas grill will work, as will a commercial kitchen environment."

Never omit the butter!  Fire it up bro!