Start by prepping the wall with a nailable surface. We used 1/2" oriented strand-board and 2" drywall screws to attach the sheathing directly to the existing studs. Keep in mind any plumbing or electrical that would need to be extended through the sheathing and firewood cladding. Because there will be small gaps between the pieces of firewood, paint the wall with flat black paint for spots that show through.
While the paint is drying, cut the firewood into 1" slices. Using a chop saw, firmly place the flat sides of the firewood against the saw table and back stop. Be extremely careful while cutting as any shift can cause the blade to bind and try to pull the piece into the saw. Safety consciousness and gear are important here. Continue cutting the wood into 1" slices. Since firewood is usually sold by the cord, every 1/10th cord should cover about 100 square feet.
Take your time nesting the pieces to each other for a tight fit. If necessary, use a chisel to shape each piece for a better fit. Continue working your way across the wall. Around any existing electrical or plumbing, be sure to give enough room for maintenance later.