Eating any amount of blueberries will improve your health and give you health benefits.
But if you're really wanting to benefit and improve your health from eating blueberries I would recommend eating at least a cup full or a bowl full of blueberries each day.
Of course you don't have to eat blueberries everyday if you don't want too.
You could also add some blueberries to pancakes or to your cereal.
Blueberries are high in antioxidants and nutrients and vitamins so eating any amount can help your health improve.
I like to add blueberries to my cereal and my pancakes as well and they make that more delicious and then sometimes I will keep a bowl of blueberries at my desk when I'm working and eat and snack on the blueberries throughout the day.
The blueberries keep my from feeling hungry and make for a healthy snack.