I worked at a smoothie shop for a few years, and by far my favorite was a mango green tea smoothie. I don't recall the exact ratio of ingredients, but it included thawed frozen mango, matcha powder, water, some of your sweetener of choice to your level of preference (mine is typically very low), ice if your blender can handle it, milk or yogurt if it can't. We did also make a coffee-style smoothie, but the owners insisted on using instant coffee powder. Same thing pretty much, a little water or milk or both, sweetener if you like it, coffee (the stronger the better), and ice. A lot of folks ordered it with chocolate syrup as a mocha style. These days I like to toss in some chia seeds or protein powder for thickener. You can even use silken tofu for some filling protein, if you're using it as a meal replacement.