DON'T wash them. The water will freeze on the blueberries and they will be a sloppy mess when you defrost them. If you feel the need to clean them rub gently between a clean dry dish towel.
Spread fresh blueberries on a cookie tray, preferably one with sides. Make sure the blueberries are in a single layer.
Freeze till firm or over night
Measure out a portion. I choose to do a 2 cup portion. I find that is what is called for in a lot of recipes. Plus that is what I need when I make blueberry pancakes!
I have a seal and vac system so that is what I use. You can use freezer storage bags or boxes.
Be sure to label them with the portion as well as the date