scrubbing, boiling, soaking and baking. If the wood is not going to the bottom of an aquarium, I would just scrub it good(no soap or anything) and bake it in the oven at 175° for a while. I've found and used plenty of wood and this has always worked for me.
I would boil and soak the wood if it is going to be placed underwater. The boiling isn't always required, IME, it just speeds up the soaking process. Which could be weeks..