We don't know if you're trying to make your smoothie thicker or thinner and a recipe would help so we know what ingredients you are using. But certainly the obvious would be less or more of the thickest ingredient and less or more of the thinnest ingredient. Add more fruit to make it thicker? Of course the flavor will always be altered but it shouldn't be to the point of not being good by making any of these changes.
"Count yourself...you ain't so many" - quote from Buck's Daddy