light sanding and then polish with wax
They can be sanded with an orbital sander. This will take out any light scratches , stains, etc.
Start out with 600 grit, then go to 800, then finish with 1000.
After that, they can be polished up with carnauba wax. I like Mothers California Gold.
You have to be careful when you are doing the sanding as to not go too deep and remove the wood grain pattern.