Step 1: Sand the HECK out of it!
Our mantel was very rough, so I really went at it with the sandpaper. I don't have any good photos of that, mostly because its exactly what it sounds like. Think you are done sanding? Nope, sand some more!
Step 2: Roll it over and over again (like a log down a hill - yes, seriously; but not seriously DOWN an actual hill); then dustbust!
This helps get the sawdust you made from sanding out of all the little crevices in the wood. Also don't fear if chunks of wood come off during this step or step 1, you want to get the rotting/dead pieces out anyway, and I promise it will just give the piece more character!
Install on your wall (we used 3 large bolts inserted into the mantel and wall). Or, if you know you want it waxed, go ahead and tackle those steps first and install at the end! Here is the photo of the before when the mental was installed and styled, but unwaxed!