Add all ingredients to the blender. I usually put the carrots at the bottom, so the blender can chop them up first - though I doubt it really matters.
Blend until smooth.
A lot of people like to use kale instead of spinach in their smoothies - and that's a great choice! Just be aware that it'll probably make your smoothie brown instead of purple. Not the most appealing color, perhaps, but it'll still taste good!