First, no matter if you are working with blueberries, strawberries, blackberries, raspberries, or any other type of berry (or grape), wash them first. Make sure there is no mold or soft discolored spots, and no dirt clinging. Trim the strawberries and remove any stems from the blueberries.
Then, use cookie sheets to lay out the berries without touching. Fit as many as you can per sheet, but make sure they are all separate. Chill the berries in the refrigerator for about 45 minutes to an hour. Then freeze them for at least 4 hours (depending on how powerful your freezer is). Once frozen, the berries can be stored in freezer bags and defrosted by the piece instead of in large clumps. Label the bags with the date and contents. (From Food Network)