Unfortunatly, there isn't a proper way to do this really.
I used to have two different types of lens for each eye, so one was blue and one was green, but now I'm on the same I cannot tell the difference for love nor money! I basically put lens A in my left eye, and cover my right eye to see how things look. Then I try lens B. Whichever looks better is, I assume, the correct lens for that eye, but there are no garuntees. You can usually tell when you have them in wrong because the world looks screwy!