If it’s wooden, scrub thoroughly after every use with very hot soapy water, then rinse with hot running water. Never leave it to soak – it’ll swell and crack. Dry with paper towels to avoid germs from a used tea towel. Leave to air, resting on its edge (it can warp if dried flat).
To get rid of strong smells, squeeze lemon juice (or sprinkle mustard powder) on the board and wipe with a clean damp cloth.
A plastic board can go in the dishwasher, but otherwise treat in exactly the same way.
Always use separate boards for raw meat and veg, and replace a cracked or badly scored board, whatever it’s made from.