I always start with a cup of Greek yogurt and a splash of whole milk. Then I add, depending on taste:
* ground flax seeds, hemp seeds or protein powder for extra nutrition
* any combo of: banana chunks, strawberries or blueberries
* any combo of: cocoa powder, banana chunks, peanut butter, honey, dark chocolate shavings
* any combo of: maple syrup, cinnamon, pumpkin pie spice, brown sugar
I've also experimented with a splash of orange juice and/or a teaspoon of orange extract (either with other fruit or cocoa). This summer, I'd like to try peaches, kiwis, and maybe pineapple chunks with coconut milk to make a "pina colada" smoothie.