To a blender, a strawberries, blueberries, kiwi fruit, yogurt, flax seed (optional), honey and ice. Blend until smooth.
If using frozen berries or if the smoothie is too thick, add just a little liquid at a time (such as water, almond milk, orange juice) until it is at the desired consistency.
Do a taste test to see if more sweetness is needed. If so, add more honey and use the pulse setting to mix.
Serve immediately while it's ice cold.