The tear-out process for reclaimed wood is more difficult than a typical tear-out. You must protect the integrity of the wood and gently loosen it from the framing instead of simply ripping it out. This takes a gentle touch and requires more patience. You can use pry bars to lever wood off of old nails, and you can use saws to free wood that cannot be torn up safely.
Once the wood has been removed from the old structure or floor, examine it thoroughly for damage. Severe structural damage -- such as deep cracks, warping or extensive water damage -- makes the board is unusable for most projects. But discoloration or surface cracks that do not extend into the heart of the board are typically not a problem because they add character to the wood.
Once a board passes inspection, remove any old nails or adhesives. In addition, remove dirt and insects from the wood. You can use steam to loosen dirt and kill bugs, or in some cases you may apply chemicals. In a smaller operation, a simple wood soap can clean up the wood and make it more presentable.
Unless you are going to use the recycled wood as-is, you must sand it down or plane it. Planing will help even out slight damage to the board and expose the original wood. This process is much quicker than sanding, but it will remove a portion of the board. For small projects, sanding with a block sander is typically more than sufficient to remove the old finish or weathering and start fresh with the revealed wood.