In the supermarket, you're most likely to find large, cultivated blueberries. Wild blueberries are much smaller and often more flavorful. Store blueberries loosely covered in the refrigerator, and use them within a day or two. Pick through fresh blueberries to remove any stems or wilted berries before rinsing and draining thoroughly.
When blueberries are abundant and inexpensive, stock up and freeze them. Arrange berries in a single layer on a baking tray and freeze them. When they're frozen, pop them into a resealable plastic freezer bag or container so you'll be able to pour out the amount needed at a later date.