There is one cardinal rule to making super healthy smoothies. No junk artificial ingredients. You should only use green vegetables and a few small servings of raw fruit or natural fruit juice to make the smoothie. The fruits just help to make the drink sweeter and more palatable. If you use a powder, be sure that the manufacturers follow these same rules. For example I love this product: Garden of Life
While this is not a huge mistake, it is still better to use good blender rather than one ill-suited for making smoothies.
The blender should have a solid base that is wide for stability. Since you're making smoothies with
your blender, it needs to have a high-speed and a 1000+ watt motor.