I make mine two different ways.  One is to use Myoplex Lite shakes with
extra water plus a teaspoon of fiber supplement and some type of extract to
enhance the flavor.  1 packet makes 2 shakes.  They don't mix well in a
shaker so I always make them in a blender and put it in the fridge.

The other way is to start with plain fat free yogurt, add splenda and
flavorings (cocoa, coffee, fruit, extracts, whatever) and fiber supplement.
I use a natural fiber supplement that has no sugar or other sweetener and
basically has the consistence and taste of sawdust but works well in a
smoothie.