The Tarot cards should be easy for the reader to use. If the reader easily mistake certain cards for another, the interpretations will prove worthless. A good note is that there should be symbols on the cards depicting which card it is. The outlook of the card(s) should also be easily understood and appealing to the reader. Usually we get drawn to some for whatever reason, but make your research upon the deck before ordering/buying.
An example is I was drawn to Aleister Crowleys Tarot deck, Thoth. This was because of the name and the beautiful illustrations on the cards. I didn't bother to make any further research and bought it. When I got it I was super eager to try it out. The next day after I soaked the cards in with energies, I surely could do pretty neat readings...but something prevented me to connect to the cards. There was always some discord while using them. This was because there were jewish/hebraic symbols on all of them. On the backside, there was a xian cross (which I just ignored at the time). After a while I had to throw the cards away. I even got enemy interference while using the cards a few times, which was unnecessary and annoying. Just be aware.