Whether you have frozen your own fresh blueberries or you buy frozen berries from the store, the skins fall apart and seem to dissolve when they start to thaw. When you are adding them to a batter, mix all other ingredients first and add the blueberries at the very end. Gently fold them into the batter as quickly as you can and do not stir any more than necessary. The more you stir them the more chance you will have of them bleeding into the batter.
When you are making something like pancakes or waffles
, cook them on one side before adding the frozen blueberries; then sprinkle a few on top just before you turn the pancakes or waffles to cook the other side.