I bought an extra pint of blueberries yesterday, so I could start stashing some away in my freezer for later use. As with other rotund berries, the technique here is to simply arrange them in one layer on a cookie sheet and then bag/store them after they’re frozen. This keeps them from clumping together.
Interestingly, I found a note explaining that you shouldn’t wash blueberries before freezing (see Step 2, here). It apparently toughens the skin. I just hope I remember to rinse them when I defrost them!