simplest method;

frozen fruit...berries, grapes, anything really...bigger fruit chopped into bits before freezing...berries can be bought frozen...

some yogurt..

and some juice...apple is nice and neutral...

estimate and blend...adding stuff to get a texture you like


The complicated method: use a recipe

a site with a list of tons of different recipes
http://www.recipesource.com/side-dishes/beverages/smoothies/indexall.html

a vegan site
http://www.sunfood.net/smoothies.html

hope this helps....