Wouldn't suggest doing anything that might actually warp the wood
For the tables you can file/sand down all the hard edges.
You can add small knicks & scratches.
Use a stain that will build up in the nicks & scratches, making them darker. You can put small bits of chain, rocks, and scrap metal in a heavy bag and use it to beat the wood.Some people use a chain to beat and distress the wood, but that can cause a regular pattern to appear.
Same techniques can be used for walls, beams, etc.
-CS