Though it may seem more hygienic (and even a bit more civilized), to slide a nice little cover on your toothbrush after brushing your teeth, it actually is not a healthy practice. Moisture gets trapped within the toothbrush cap, keeps your toothbrush bristles from drying out and promotes bacterial growth.
Place it in a dry, open space where the toothbrush can breathe. Store it upright so it drys out completely.
Even though its convenient, the right storage area shouldn’t be near the sink or lavatory. Every time you flush, bacteria can travel through the air and land on your toothbrush, the same goes for splashes of dirty, soapy water. For clean and healthy toothbrush storage it’s best to use a place in your bathroom cabinet.