It is easiest to clean wooden spoons if you do it immediately after use, before food has time to dry on them.
If spoons develop a musty odor, clean them well with dish soap and a teaspoon of baking soda added to the dishwater.
Avoid using wooden spoons to stir raw meats (including eggs) or other foods that are common sources of food poisoning. Bacteria may get into tiny cracks in the spoon and multiply.
Do not clean wooden spoons in the dishwasher. The detergent and the heat can cause the spoons to warp or crack.