There are indefinite combinations you can use in your smoothie-making, but coming up with the perfect ratio of nutritious, delicious, and not over the caloric or carbohydrate guidelines you've set for yourself is a bit more complicated.
In the same vein as "keep it simple salad", I bring you the keep it simple smoothie.
HERE IT IS:
Serving: smoothie for one (or pour half into a your favorite tumbler or smoothie shaker to enjoy it again later)
1 soft fruit or veggie: depending on your goals, choose something like an avocado, handful of greens, or banana
1 cup of frozen fruit: fresh frozen bags of mixed berries or citrus will do the trick
1 nutrition boost: protein powder (pea and hemp are great vegan options; whey is easy to find), super greens, or 1 tablespoon of your favorite nut butter, nuts, or seeds
1 1/2 cups liquid: milk (coconut, almond, dairy), kefir, greek yogurt (with this option, add 1 cup liquid and 1/2 cup yogurt for ideal consistency), or water
OPTIONAL: Many people will find the natural sweetness of the fruit to be enough, but if your smoothie needs a little something more, toss in 1-2 dates, a drop of honey, or stevia to taste