These are the basic ingredients I use whenever making a basic smoothie:
Frozen Strawberries・Frozen Raspberries・Frozen Blueberries・Banana・Greek Yogurt・Spinach
Some other ingredients you may want to try adding are:
Blackberries・Mangoes・Peaches・Clementines・Grapes・Kiwis・Pomegranate Seeds・Kale・Protein Powder・Flax Seed
In the smoothie pictured above I used a mango in addition to all of the basic ingredients. If I ever need to add any liquid I try to stick with water to keep the calories as low as possible.