Let's start with the fact that I'm not too into the concept of "should" when it comes to rules for readings. I believe the best reading comes from a style that seamlessly fits your personality and therefore helps you to focus and recite your inner vision. A reading style/technique, for me, is something that assists, is congruent with, and is not the focus of the reading, itself.
Okay, enough of the soapbox.
When I read with The Deck of Shadows, I ALWAYS include the Urim and Thummim cards. For me these are more than mere "Joker" cards and, in fact, serve a purpose for more than just "yes or no" readings. In creating the cards, themselves, I was well aware of the various translations for these words - interpretations that are reflect on the other "words" that are displayed. Essentially, you will see a pattern; namely, Thummim can be used in a reading to represent "what is real" or "what is confirmed" or "what is beginning." Urim, then, can be used as "what is revealed/no longer hidden" or "what you need to know" or "what is ending." This allows these particular cards to serve as a sort of confirmation or rejection tool for the other cards.
To say it another way, if Thummim appears in a reading, it is an indication that the companion cards are, in fact, valid. If Urim appears, then a negative connotation (almost like a reversal) is indicated.
Now, here is something really exciting to try: during a reading, take the Thummim and Urim cards from the deck and hand them to the person receiving the reading. Have them place the two cards into the shuffled/mixed deck FACE-UP. Then spread the face-down deck and locate the two face-up cards. Take out the face-down card that is immediately above each face-up card. The face-down cards are turned over and read in conjunction with the face-up indicators. In other words, the card that is immediately above/next to Thummim is used to show what is just beginning. The card that is immediately above-next to Urim is used to show what is just ending.
Of course, any of the attributes for Thummim and Urim can be used in this way. I happen to use Thummim and Urim in a "What is Real/What is Not" reading.
Just some thoughts. Enjoy. - Scott