Get someone to give you a hand,

Stand with your arm out to the side.

Hold some good quality water.

Have someone apply slowly increasing pressure on your arm until they get movement.
(you resist - don't have to fight it just resist)

now

Hold the product in your hand (some say against your chest - works either way in my experience)

have them apply slowly increasing pressure until they get movement (resist again)

see how the body reacts.

-
you should really gage to make sure you are getting clear responses first.

Say your name and have them test you
then say "my name is Fred Flinstone

if you can feel the difference and your name is strong and the lie is weak then you proceed with testing the product - always get a comparison...say water for example

there is more to it but that is basic muscle testing (there is a thread on this)

there are quite a few naturopaths that use this to check all suppliments and foods etc for a personal program..

I use it with almost every client (I do it a different way - the arm is just easiest to discribe)... and I only use it cause it gets results... I get info that sometimes people respond to with "I've never told anyone about that in my life"

A little practice and it is pretty easy to at least look at the foods and products you want to take.