All you need to do is just REALLY READ MINDS.
Spector think of a card and you divine it. Direct and simple.
RUM also allows you to perform ACAAN(Any Card At Any Number) with an Ordinary deck of cards. Spectator just have to think of ANY card and name ANY number they want, and NOTHING is written down.you don't even need to know what card they thought of.
This is not the most easiest things you can do,but it can be your go to effect and it also can be your reputation maker once you get it down.
What others are saying:
"Aaron has created a very effective method for the Think Of A Card plot,I will be using this!"
Once you tried it by yourself, you will not believe your eyes that how clean it is. This is one of the most purest routine I've ever seen in mentalism