Take one grapefruit, rip out the flesh and toss into a blender. Our just buy a jar of peeled grapefruit.
Toss 3/4 cup of strawberries into a blender. (Don't need to remove the leaves/stem.)
Add 1 or two bananas.
Blend. Pour into a cup and drink.
I know some people use apples instead of bananas but personally I find it's easier to use bananas and it tastes far better. You don't need to core and peel apples and bananas just get sweeter when they get black spots on them.