Bananas get sweeter as they ripen. The riper the better until almost a brown shell or at least spotted brown. Freeze bananas overnight if possible for a smoothie. They way you need less ice and it stays thick. Simple recipe is
1 ripe banana
1/2 cup non-fat yogurt
1 tbs honey
1 cup ice, crushed
Throw it in a blender. Use less ice if banana is frozen. Try to cut or break the banana if possible. Add milk just to keep it liquid in the blender. If you have a teaspoon of vanilla, that is extra good also.
Adding 1/2 cup of orange juice is good in an evening smoothie.